Cutting element apparatuses, drill bits including same, methods of cutting, and methods of rotating a cutting element

ABSTRACT

A subterranean drilling system may include a drill string and a rotary drill bit coupled to the drill string. The rotary drill bit may include a bit body and a cutting element coupled to the bit body, with the cutting element being structured to rotate in response to torque applied to the cutting element. The system also may include a cam assembly coupled to the drill string, a cam follower assembly in contact with a cam surface of the cam assembly, and a torque-applying structure coupled to the cam follower assembly. The torque-applying structure may be configured to apply torque to the cutting element in response to relative rotation between the cam assembly and the cam follower assembly.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of prior U.S. applicationSer. No. 11/247,574, filed 11 Oct. 2005, the disclosure of which isincorporated, in its entirety, by this reference.

FIELD OF THE INVENTION

The present invention relates generally to cutting elements. Morespecifically, the present invention relates to methods and apparatusesfor applying torque to a cutting element to rotate the cutting elementwhile cutting a material.

BACKGROUND

Cutting elements have been utilized for a variety of material removalprocesses such as machining, cutting, and drilling. For example,tungsten carbide cutting elements have been used for machining metalsand, to some degree, on drilling tools for drilling subterraneanformations, as known in the art. Further, polycrystalline diamondcompact (PDC) cutters have been employed for machining metals (e.g.,non-ferrous metals, usually) and for subterranean drilling tools, suchas, drill bits, reamers, core bits, etc. Of course, other types ofcutting elements have been utilized for cutting operations, for example,ceramic (cubic boron nitride, silicon carbide, etc.) cutting elements orother cutting elements as known in the art.

For example, it is known to perform lathe operations with a cuttingelement (e.g., PDC cutter, a tungsten carbide cutting element, oranother cutting element as known in the art). Additionally, somemachinery (i.e., a planer) is designed to remove or cut material along aselected plane by moving a the piece to be cut against a cuttingelement. In some configurations, the piece to be cut may be rotated andthe cutting element may be radially moved to plane or face a surface ofthe material. Such machinery may be utilized, among other examples, forforming monuments or building materials (e.g., any rock formation, suchas granite, marble, etc.).

More particularly, with respect to subterranean drilling, rotary drillbits employing cutting elements for drilling subterranean formations,such as polycrystalline diamond compact (PDC) cutters, have beenemployed for several decades. Although other configurations are known inthe art, PDC cutters are typically comprised of a disc-shaped diamond“table” formed on and bonded (under high-pressure and high-temperatureconditions) to a supporting substrate, such as a cemented tungstencarbide (WC) substrate.

As known in the art, the drill bit bodies to which cutting elements areattached may often be formed of steel or of molded tungsten carbide.Drill bit bodies formed of molded tungsten carbide (so-calledmatrix-type bit bodies) are typically fabricated by preparing a moldthat embodies the inverse of the desired topographic features of thedrill bit body to be formed. Examples of such topographic featuresinclude generally radially extending blades, sockets or pockets foraccepting the cutting elements, junk slots, internal watercourses,passages for delivery of drilling fluid to the bit face, ridges, lands,and the like. Tungsten carbide particles are then placed into the moldand a binder material, such as a metal including copper and tin, ismelted or infiltrated into the tungsten carbide particles and solidifiedto form the drill bit body. Steel drill bit bodies, on the other hand,are typically fabricated by machining a piece of steel to form thedesired external topographic features of the drill bit body. In bothmatrix-type and steel bodied drill bits, a threaded pin connection maybe formed for securing the drill bit body to the drive shaft of adownhole motor or directly to drill collars at the distal end of a drillstring rotated at the surface by a rotary table or top drive.

Cutting elements are typically attached to matrix-type and steel bodieddrill bits by either brazing or press-fitting the cutting elements intorecesses or pockets formed in the bit face or in blades extending fromthe face. The cutting elements are attached to the bit bodies in thismanner to ensure sufficient cutting element retention, as well asmechanical strength sufficient to withstand the forces experiencedduring drilling operations. However, conventional drill bits havingconventionally attached cutting elements suffer from a number ofdrawbacks and disadvantages. For example, because the cutting element isaffixed to the bit body, only a portion of the circumferential cuttingedge of the cutting element actually engages the subterranean formationbeing drilled. The constant engagement between this select portion ofthe cutting edge and the formation tends to quickly degrade and weardown the engaged portion of the cutting edge, resulting in decreasedcutting element life, drilling efficiency, and accuracy. This constantengagement also significantly increases the temperature of the cuttingelement, which may further result in increased wear and/or potentialdestruction of the cutting element and drill bit body.

Accordingly, a number of conventional attempts have been made to providea drill bit having cutting elements that are free to rotate duringdrilling due to interaction with a subterranean formation. For example,U.S. Pat. No. 4,553,615 to Grainger (the '615 patent) discloses a rotarydrilling drag bit having a cutting element having a spindle formed ofcemented tungsten carbide mounted in a recess formed in the face of abit blade. A similar configuration is disclosed in U.S. Pat. No.4,222,446 to Vasek.

However, unpredictability of the nature of contact with the formationbeing drilled, extreme temperatures, forces, and pressures encounteredin subterranean drilling environments may prevent or inhibit rotation ofthe cutting elements altogether. Thus, such a conventional cuttingelement, as with brazed or press-fit cutting elements, may exhibit aportion of the cutting edge that tends to degrade and wear down,resulting in decreased cutting element life and drilling efficiency.Similarly, when machining, wear that occurs relative to a cuttingelement may cause interruptions in the machining operation to replace orotherwise reorient the cutting element.

Accordingly, there exists a need for methods and apparatuses forrotating a cutting element during cutting of a material. The torqueapplied to the cutting element would be sufficient to rotate, eithercontinuously or periodically, the cutting element during cutting of amaterial.

SUMMARY

In at least one embodiment, a rotary drill bit for drilling asubterranean formation may comprise a bit body and at least one cuttingelement coupled to the bit body. Further, the at least one cuttingelement may comprise a table bonded to a substrate, and atorque-generating assembly may be configured to apply torque to thesubstrate of the at least one cutting element. The torque-generatingassembly may be powered by the rotary motion of the rotary drill bit ormay be hydraulically or electrically powered. In addition, thetorque-generating assembly may generate and apply torque to the cuttingelement either continuously or periodically and may comprise an actuatorassembly, such as an electric motor assembly, a hydraulic pump assembly,and/or a cam assembly. In certain embodiments, a structural assemblytransmits the mechanical motion generated by the actuator assembly tothe cutting element. According to one embodiment, the structuralassembly comprises a rack coupled to the actuator assembly and a pinionoperably coupled to both the rack and a drive shaft affixed to thecutting element.

In one aspect of the invention, a cutting element assembly may compriseat least one cutting element having a table bonded to a substrate and atorque-generating assembly coupled to the at least one cutting elementand configured for applying torque to the cutting element. In a furtheraspect of the invention, a cutting element may comprise a substrate, atable of superabrasive material disposed on an end of the substrate andat least one impelling feature formed into at least a portion of anexterior surface of the substrate.

In addition, yet another aspect of the invention relates to a method ofrotating a cutting element coupled to a drill bit for drilling asubterranean formation. More specifically, a cutting element may beprovided comprising a table bonded to a substrate and the substrate ofthe cutting element may be coupled to a drill bit body. Also, torque maybe applied to the substrate of the cutting element. A method of drillinga subterranean formation may comprise providing a cutting elementcomprising a table bonded to a substrate, coupling the cutting elementto a drill bit, engaging the subterranean formation with the cuttingelement, and applying torque to the cutting element.

Further, another aspect of the present invention relates to a method ofcutting a material, the method comprising: providing a cutting elementcomprising a table bonded to a substrate; cutting a material with thecutting element; and rotating the cutting element by applying torque tothe substrate of the cutting element while cutting the material with thecutting element.

In an additional embodiment, a subterranean drilling system may comprisea drill string and a rotary drill bit coupled to the drill string. Therotary drill bit may comprise a bit body and a cutting element coupledto the bit body. The cutting element may be structured to rotate inresponse to torque applied to the cutting element. The system also maycomprise a cam assembly coupled to the drill string, a cam followerassembly in contact with a cam surface of the cam assembly, and atorque-applying structure coupled to the cam follower assembly. Incertain embodiments, the torque-applying structure may be configured toapply torque to the cutting element in response to relative rotationbetween the cam assembly and the cam follower assembly.

In one embodiment, the cutting element may comprise at least oneengaging feature and the torque-applying structure may be a push rodhaving a first end disposed within a recess defined in the cam followerassembly and a second end structured to engage the at least one engagingfeature of the cutting element. The first end of the push rod maycomprise a superabrasive material.

In certain embodiments, the cam follower assembly may comprise at leastone cam follower element. This cam follower element may comprise asubstrate and a superabrasive table bonded to the substrate. Inaddition, at least a portion of the cam follower assembly may bepivotably attached to the bit body. At least a portion of the camfollower assembly also may be rotatably attached to at least a portionof the torque-applying structure. In certain embodiments at least aportion of the cam follower assembly may pivot in response to relativerotation between the cam assembly and the cam follower assembly and atleast a portion of the torque-applying structure may rotate in responseto relative rotation between the cam assembly and the cam followerassembly.

In one embodiment, the push rod may be biased toward the cam followerassembly. The push rod also may comprise a flexible portion and asubstantially rigid portion. In addition, the cutting element may belimited from rotating in a selected direction. The torque-applyingstructure also may apply torque to the cutting element in periodicincrements, causing the cutting element to rotate in periodicincrements. The cutting element also may rotate within an angle ofrotation of less than 360 degrees.

In certain embodiments, the drilling system may further comprise apressure-compensating assembly. This pressure-compensating assembly maybe structured to at least partially compensate for differences between apressure within at least a portion of the drill bit and another pressureexternal to at least a portion of the drill bit. Thepressure-compensating assembly also may comprise a lubricating fluidwithin a sealed chamber that is defined by at least one seal member anda dynamic member that is structured to move in response to changes inpressure external to the sealed chamber.

In one embodiment, the cam assembly may comprise a plurality of caminserts each affixed to a cam body, the plurality of cam insertscomprising at least a portion of the cam surface. At least one caminsert of the plurality of cam inserts may at least partially surroundan adjacent cam insert. In addition, the plurality of cam inserts may besubstantially identical.

In certain embodiments, the cam assembly may comprise a cam body havinga substantially planar bottom surface. In addition, the cam surface ofthe cam assembly may be angled with respect to the substantially planarbottom surface of the cam body. The cam assembly also may comprise asubstantially annular-shaped cam body having an external surface and aninternal surface. In addition, a distance between the external surfaceand the internal surface of the cam body may vary at different points onthe cam body.

In one embodiment, a rotary drill bit for drilling a subterraneanformation may comprise a bit body and a cutting element coupled to thebit body and structured to rotate in response to torque applied to thecutting element. The cutting element may comprise a first portion asecond portion mechanically coupled to the first portion. The firstportion of the cutting element may be structured to decouple from thesecond portion of the cutting element when a cutting force applied tothe first portion exceeds a selected magnitude.

In certain embodiments, the second portion of the cutting element maycomprise at least one engaging structure structured to engage at leastone engaging structure of the first portion of the cutting element. Inaddition, the first portion of the cutting element may comprise asuperabrasive table bonded to a substrate. The second portion of thecutting element also may comprise a friction material structured toengage a friction material of the first portion of the cutting element.

In one embodiment, a subterranean drilling system may comprise a rotarydrill bit comprising a bit body and a cutting element coupled to the bitbody, the cutting element being structured to rotate in response totorque applied to the cutting element. The system also may comprise atorque-amplifying assembly operably coupled to the cutting element and atorque-generating assembly structured to apply a selected torque to thetorque-amplifying assembly. In certain embodiments, thetorque-amplifying assembly may apply a torque in excess of the selectedtorque to the cutting element.

The torque-amplifying assembly may comprise a first gear coupled to thetorque-generating assembly, the first gear comprising a plurality ofteeth, and a second gear engaged with the first gear, the second gearcomprising a plurality of teeth. In one embodiment, the number of teethon the second gear may be different than the number of teeth on thefirst gear.

In certain embodiments, a subterranean drilling system may comprise atorque-generating assembly and a rotary drill bit comprising a bit bodyand a plurality of rotatable cutting elements coupled to both the bitbody and the torque-generating assembly. In one embodiment, each of theplurality of rotatable cutting elements may rotate in response to torqueapplied by the torque-generating assembly. In addition, thetorque-generating assembly may comprise at least one engaging featurethat is structured to engage at least one engaging feature provided onat least one of the plurality of rotatable cutting elements.

In one embodiment, a rotary drill bit for drilling a subterraneanformation may comprise a bit body, a coupling structure, and a cuttingelement. The cutting element may comprise a non-ferrous portion having atop surface and a bottom surface and a ferrous portion bonded to thebottom surface of the non-ferrous portion. In certain embodiments, theferrous portion may be structured to be threadedly coupled to thecoupling structure to couple the cutting element to the bit body.

In one embodiment, the ferrous portion may comprise steel. In addition,at least a portion of the ferrous portion may be coated with an erosionresistant material. The erosion resistant material also may comprisetungsten carbide.

In certain embodiments, a rotary drill bit for drilling a subterraneanformation may comprise a bit body, a cutting element coupled to the bitbody, the cutting element being structured to rotate in response totorque applied to the cutting element, a hydraulic actuator assembly,and a structural assembly coupling the hydraulic actuator assembly tothe cutting element. In one embodiment, the structural assembly may beconfigured to apply torque to the cutting element by converting linearmotion generated by the hydraulic actuator assembly into rotary motion.

The hydraulic actuator assembly may comprise a pump, a chamber definedin the bit body, the chamber being in fluid communication with the pump,a piston disposed within the chamber, the piston moveable between afirst position and a second position, and a piston rod coupled to thepiston. The structural assembly may comprise a connecting structurecoupled to the piston rod and a crank rotatably attached to theconnecting structure.

In one embodiment, a subterranean drilling system may comprise a drillstring and a rotary drill bit coupled to the drill string. The rotarydrill bit may comprise a bit body, a first cutting element coupled tothe bit body, the first cutting element being structured to rotate inresponse to torque applied to the cutting element, and a second cuttingelement coupled to the bit body; the second cutting element beingstructured to remain in a fixed position relative to the bit body. Thesystem also may comprise a cam assembly coupled to the drill string, thecam assembly comprising a cam surface, a cam follower assembly incontact with the cam surface of the cam assembly, and a torque-applyingstructure coupled to the cam follower assembly. In certain embodiments,the torque-applying structure may be configured to apply torque to thefirst cutting element in response to relative rotation between the camassembly and the cam follower assembly.

Features from any of the above-mentioned embodiments may be used incombination with one another in accordance with the present invention.These and other embodiments, features and advantages will be more fullyunderstood upon reading the following detailed description inconjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary embodiments of thepresent invention and are a part of the specification. Together with thefollowing description, the drawings demonstrate and explain aspects ofthe present invention.

FIG. 1A shows a schematic representation of a cutting element used forcutting a material.

FIG. 1B shows a perspective view of a cutting element.

FIG. 1C shows a perspective view of a cutting element and a selectedangle θ within which the cutting element may be rotated.

FIG. 1D shows a schematic view of a cutting element used for cutting amaterial, the cutting element supported by a body.

FIG. 2 shows a schematic, side cross-sectional view of an exemplarydrilling apparatus and drill bit employing an actuator assembly forapplying torque to a rotatable cutting element.

FIG. 3 shows an enlarged schematic view of an exemplary rotary drill bitemploying an actuator assembly for applying torque to a rotatablecutting element.

FIG. 4A shows an enlarged cross-sectional view of an exemplary actuatorand structural assembly for applying torque to a rotatable cuttingelement.

FIG. 4B shows an enlarged cross-sectional view of the exemplary actuatorand structural assembly illustrated in FIG. 3A, as taken along the line3B.

FIG. 4C shows a schematic perspective view of an actuator assembly forrotating a cutting element including a substrate comprising engagingfeatures.

FIG. 4D shows a schematic top elevation view of the actuator assemblyand cutting element shown in FIG. 4C.

FIG. 5 shows a schematic, side cross-sectional view of an alternativeembodiment of a rotary drill bit employing an actuator assembly forapplying torque to a rotatable cutting element.

FIG. 6 shows an enlarged cross-sectional view of an additionalembodiment of a motor for applying torque to a rotatable cuttingelement.

FIG. 7 shows an enlarged cross-sectional view of an additionalembodiment of an actuator assembly for applying torque to a rotatablecutting element.

FIG. 8A shows a side cross-sectional view of an exemplary embodiment ofa rotating sleeve assembly for applying torque to a cutting element.

FIG. 8B shows a perspective view of a cam assembly employed by therotating sleeve assembly illustrated in FIG. 8A.

FIG. 8C shows a side view of the cam assembly illustrated in FIG. 8B.

FIG. 9 shows a chart illustrating test data generated by conventionalcutting elements and a cutting element according to the presentinvention.

FIG. 10 shows an enlarged view of a rotatable cutting element having animpelling feature.

FIG. 11A is a perspective side view of an exemplary drilling systemaccording to an additional embodiment.

FIG. 11B is a top view of the exemplary drilling system illustrated inFIG. 11A.

FIG. 12A is a perspective side view of an exemplary cutting element andtorque-applying structure according to an additional embodiment.

FIG. 12B is an additional perspective view of the exemplary cuttingelement and torque-applying structure illustrated in FIG. 12A.

FIG. 12C is a perspective view of a torque-applying structure comprisinga flexible portion and a substantially rigid portion according to atleast one embodiment.

FIG. 13A is a top view of an exemplary cam assembly according to atleast one embodiment.

FIG. 13B is a perspective view of an exemplary cam insert according toat least one embodiment.

FIG. 13C is a side view of the exemplary cam assembly illustrated inFIG. 13A.

FIG. 13D is a perspective view of the exemplary cam assembly illustratedin FIG. 13A.

FIG. 14A is a top view of an exemplary cam follower assembly accordingto at least one embodiment.

FIG. 14B is a side view of the exemplary cam follower assemblyillustrated in FIG. 14A.

FIG. 14C is a perspective view of an exemplary cam follower elementaccording to at least one embodiment.

FIG. 15A is a cross-sectional side view of an exemplary cam followerassembly and torque-applying structure according to at least oneembodiment.

FIG. 15B is a perspective side view of a cam follower assembly andtorque-applying structure according to an additional embodiment.

FIG. 16A is a perspective side view of an exemplary cutting element andtorque-applying structure according to an additional embodiment.

FIG. 16B is an illustration of the exemplary cutting element andtorque-applying structure illustrated in FIG. 16A.

FIG. 16C is a cross-sectional side view of a cutting element accordingto an additional embodiment.

FIG. 17 is a cross-sectional side view of an exemplary cutting elementaccording to an additional embodiment.

FIG. 18A is a cross-sectional side view of an exemplary cutting element,torque-amplifying assembly, and torque-applying structure according toat least one embodiment.

FIG. 18B is a cross-sectional view of a portion of the exemplarytorque-amplifying structure illustrated in FIG. 18A.

FIG. 19 is a perspective side view of an exemplary cutting elementassembly and torque-applying structure according to an additionalembodiment.

FIG. 20 is a cross-sectional side view of an exemplary bit body andtorque-applying structure according to an additional embodiment.

FIG. 21A is a side view of an exemplary drilling system according to anadditional embodiment.

FIG. 21B is a cutaway perspective view of a portion of the exemplarydrilling system illustrated in FIG. 21A.

FIG. 21C is a perspective side view of a portion of the exemplarydrilling system illustrated in FIG. 21A.

FIG. 21D is a perspective side view of a portion of the exemplarydrilling system illustrated in FIG. 21A.

FIG. 21E is a top view of an exemplary cam assembly according to atleast one embodiment.

FIG. 21F is a perspective view of the exemplary cam assembly illustratedin FIG. 21F.

FIG. 22A is a side view of an exemplary drilling system according to anadditional embodiment.

FIG. 22B is a perspective side view of an exemplary hydraulic actuatorassembly according to an additional embodiment.

Throughout the drawings, identical reference characters and descriptionsindicate similar, but not necessarily identical elements. While thepresent invention is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,one of skill in the art will understand that the present invention isnot intended to be limited to the particular forms disclosed. Rather,the invention covers all modifications, equivalents and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION

For ease of use, the words “including” and “having,” as used in thespecification and claims, are interchangeable with and have the samemeaning as the word “comprising.” In addition, as used throughout thespecification and claims, the word “cutting” generally refers to anydrilling, boring, or the like. The word “cutting,” as used herein,refers broadly to machining processes, drilling processes, or any othermaterial removal process utilizing a cutting element.

Generally speaking, the present invention relates to applying a torqueto a cutting element during a cutting process. More particularly, acutting element may be rotated during a cutting process so that acutting edge is moved during the cutting process. For example, as shownin FIG. 1A, a cutting element 10 may be used for cutting a material 12.Cutting element 10 may comprise, as shown in FIG. 1A, a substrate 18bonded to a superhard table 20 (e.g., polycrystalline diamond). Thus, inone embodiment, cutting element 10 may comprise a PDC cutter. In furtherdetail, cutting edge 15 of cutting element 10 may be forced againstmaterial 12 so that cuttings 34 are removed from surface 30 and cutsurface 32 is formed. Cuttings 34 are shown (collectively in thedrawings) as a so-called “chip.” It is understood that the cuttings maycomprise pulverized material, fractured material, sheared material, acontinuous chip, or any cuttings produced as known in the art, withoutlimitation. According to one aspect of the present invention, cuttingelement 10 may be rotated during the process of cutting material 12.Such rotation may introduce a greater portion of a cutting edge 15 ofcutting element 10 against material 12, which may reduce wear of thecutting element 10. For example, cutting element 10 may be rotated byapplying a torque (labeled “T” in FIGS. 1B and 1C) to substrate 18 ofthe cutting element 10. In one embodiment, cutting element 10 may besubstantially cylindrical and may rotate about central axis 11. FIG. 1Bshows another view of cutting element 10. As shown in FIG. 1B, cuttingedge 15 (located generally at radius r from central axis 11) may beformed about the circumference of cutting face 14, which may besubstantially planar. In addition, as known in the art, cutting edge 15may include at least one chamfer, at least one so-called buttressgeometry, or any other geometry as known in the art. Further, cuttingelement 10 may be rotated about central axis 11 in a direction of theapplied torque T in a direction CW (i. e., clockwise), in a directionlabeled CCW (i.e., counter-clockwise), or both (e.g., one direction at atime). Such rotation may cause a selected portion of cutting edge 15 tocontact a material (e.g., material 12, as shown in FIG. 1A) cut withcutting element 10. For example, FIG. 1C shows cutting element 10 and aportion of cutting edge 15 encompassed by angle θ. Thus, it may beappreciated that cutting element 10 may be rotated in directions CW andCCW so that a selected region of cutting edge 15 encompassed by angle θis moved into cutting engagement with a material. Of course, the cuttingelement may be rotated in at least one direction, substantiallycontinuously or intermittently, so that the entire cutting edgeinteracts with a material being cut during a cutting process. Of course,it may further be appreciated that cutting element 10 must be supportedto resist against the forces of the cutting process. As shown in FIG.1D, the present invention contemplates that, in one embodiment, acutting element 10 may be supported, at least in part, by a body 40(e.g., a bit blade, a cutting element holding base, a lathe cuttingelement base, a planer cutting element base, etc.).

In addition, one aspect and application of the present invention relatesto apparatuses and methods for applying torque to a cutting element inorder to rotate the cutting element relative to a drill bit body. FIG. 2is a schematic side cross-sectional view of an exemplary drillingapparatus and drill bit employing an actuator assembly for applyingtorque to a rotatable cutting element. As seen in the exemplaryembodiment illustrated in FIG. 2, exemplary drilling apparatus 100generally comprises a drill bit 102 having a tapered shank 104 threadedonto a drill string 106, as known in the art. Drill bit 102 generallyrepresents any number of earth-boring or drilling tools, including, forexample, core bits, roller-cone bits, fixed-cutter bits, eccentric bits,bicenter bits, reamers, reamer wings, and the like. In at least oneembodiment, drill bit 102 comprises a plurality of radially andlongitudinally extending blades 112 defining a leading end for drillinginto a subterranean structure. Circumferentially adjacent blades 112 maydefine a plurality of so-called junk slots therebetween for channelingformation cuttings away from a face 114 of drill bit 102. As will beknown to those of skill in the art, drill bit 102 may be formed in anynumber of ways and of any number of materials. For example, drill bit102 may be machined from steel or may be manufactured by infiltrating abinder of tungsten carbide particulate, as described above.

As shown in FIG. 2, drilling fluids F may be pumped through a bore 108formed in drill string 106 and into a plenum 118 defined within drillbit 102. As known in the art, at least one passageway 117 defined withindrill bit 102 may communicate drilling fluids F to one or more apertures116 formed in face 114 of drill bit 102. Drilling fluids F emanatingfrom apertures 116 promote flushing formation cuttings away from face114 while simultaneously cooling blades 112 and cutting elements 170.

According to at least one embodiment, one or more rotatable cuttingelements 170 may be mounted to drill bit 102 (e.g., to face 114 or blade112). Generally speaking, each of cutting elements 170 may comprise anycutting element known in the art capable of cutting a subterraneanformation, including, for example, a PDC cutter. As seen in theexemplary embodiment illustrated in FIG. 4A, a cutting element 170 maycomprise a layer or table 174 bonded to or formed upon a substrate 172.Table 174 may be formed of any number of materials used for cuttingformations, including, for example, a superhard or superabrasivematerial such as polycrystalline diamond. “Superhard,” as used herein,refers to any material having a hardness that is at least equal to ahardness of tungsten carbide. Similarly, substrate 172 may comprise anynumber of materials capable of adequately supporting a superabrasivematerial during drilling of a subterranean formation, including, forexample, cemented tungsten carbide. For example, cutting element 170 mayinclude a table 174 comprising polycrystalline diamond bonded to asubstrate 172 comprising cobalt-cemented tungsten carbide. In such aconfiguration, table 174 and substrate 172 may be manufactured accordingto processes known in the art. Optionally, after formation of table 174,a catalyst material (e.g., cobalt, nickel, etc.) may be at leastpartially removed (e.g., by acid-leaching) from table 174.

The present invention contemplates that cutting elements 170 may berotatably mounted to face 114 or blades 112 of drill bit 102 in anynumber of ways and configurations. For example, in at least oneembodiment a recess 178 may be defined within substrate 172 so as toretain the distal end of a structural member rotatably attached to atorque-generating assembly housed in drill bit 102. Additional examplesof structures for coupling a shaft to a substrate are disclosed in U.S.patent application Ser. No. 11/148,806, filed Jun. 9, 2005, thedisclosure of which is incorporated, in its entirety, by this reference.Any of such structures or other suitable structures as known in the artfor coupling a shaft to a substrate may be employed to couple substrate172 to shaft 176, as shown in FIG. 4A. In further detail, in theexemplary embodiment illustrated in FIG. 4A, recess 178 is defined tohave a tapered cross-section that embodies the inverse of the shape ofthe distal end of a drive shaft 176 rotatably attached to atorque-generating assembly (e.g., actuator assembly 140) housed in drillbit 102. Although recess 178 may be formed in any number of sizes orshapes, recess 178 may be formed to exhibit a tapered cross-sectionalsize that decreases in width in a direction away from table 174. Thissubstantially frustoconical configuration may provide a robust structurefor mechanically retaining the distal end of drive shaft 176 withinsubstrate 172 of cutting element 170. Further, such a configuration mayrotatably couple cutting element 170 to a torque-generating assembly(e.g., actuator assembly 140) housed in drill bit 102 (FIG. 2). Infurther detail, cutting element 170 may be mechanically coupled to arotatable structural assembly (e.g., drive shaft 176). Accordingly, suchmechanical coupling may avoid thermal damage to cutting element 170associated with conventional brazing techniques.

Referring to FIG. 4A, in one embodiment, each of cutting elements 170may be rotatably mounted to drill bit 102 by adhering, brazing, welding,or otherwise mechanically affixing substrate 172 of each of cuttingelements 170 to a rotatable structural assembly (e.g., drive shaft 176)attached to a torque-generating assembly (e.g., actuator assembly 140)housed in drill bit 102. For example, the inner surface of recess 178defined in substrate 172 may be threaded so as to house a structuralassembly (e.g., drive shaft 176) having a complimentary threaded outersurface. In another embodiment, each of cutting elements 170 may berotatably mounted to drill bit 102 in a manner similar to that disclosedin U.S. Pat. No. 4,553,615 to Grainger, the entirety of the disclosureof which is hereby incorporated by this reference. For example, cuttingelement 170 may include a spindle that is rotatably held in a cuttingpocket 15 formed in blade 112 by a resilient split ring (i.e., a lockring) fitted into a peripheral groove formed along the spindle.

According to certain embodiments, each of cutting elements 170 isrotatably mounted within a respective cutting pocket 115 defined in bitblade 112 of drill bit 102. Cutting pocket 115 of bit blade 112 may begenerally configured for surrounding at least a portion of the substrate172 of cutting element 170. As seen in FIG. 4A, the uppermost edge ortip of table 174 of each of cutting elements 170 may be positioned toextend beyond the upper surface of bit blade 112. Such clearance may bedesirable so that each of cutting elements 170 contact the subterraneanformation to be drilled, thus cutting and removing material from theformation. A portion of the upper surface of bit blade 112 may bestructured for contacting a subterranean formation during drilling tolimit a depth-of-cut (i.e., a rate-of-penetration) of a cutting elementassociated therewith, as known in the art. In addition, optionally, eachof cutting elements 170 may be oriented to exhibit a so-called“negative” back rake angle, a side rake angle, or both, as known in theart. Further, each of cutting elements 170 (table 174, substrate 122, orboth) may include a chamfer or buttress or may embody any other cuttingedge geometry known in the art, without limitation.

In addition, still referring to the exemplary embodiments illustrated inFIGS. 2 and 3, drilling apparatus 100 may further comprise a motor 120for powering a pump 130. Motor 120 may be configured to convert themomentum or energy of drilling fluids F into torque to rotate outputshaft 125 connected to pump 130. For example, motor 120 may comprise apositive displacement motor for converting the momentum or energy ofdrilling fluids F flowing through bore 108 in drill string 106 intotorque or a force or a moment for rotating output shaft 125, as known inthe art. Alternatively, motor 120 may comprise any other configurationor motor capable of driving pump 130, including, for example, aMoineau-type motor, a turbine-type motor, or the like.

In at least one embodiment, pump 130 may be configured to generatepressure (via mechanical energy generated by motor 120) for operating anactuator assembly 140. Pump 130 may comprise any form of pump devicecapable of operating actuator assembly 140, including, for example, ahydraulic or pneumatic pump such as a gear, vane, or piston pump. In theexemplary embodiment illustrated in FIG. 3, a control valve assembly 135is configured to control the flow, pressure, or both, of fluid betweenpump 130 and actuator assembly 140. Control valve assembly 135 maycomprise any form of valve or other structure capable of controlling theflow and/or pressure of fluids between pump 130 and actuator assembly140 (and vice versa). For example, control valve assembly 135 maycomprise one or more angle valve, ball valve, block and bleed valve,control valve, directional valve, drain valve, poppet valve, solenoidvalve, spool valve, or the like. Control valve assembly 135 may alsocomprise so-called “double-port” or “multi-port” hydraulic or pneumaticvalve configurations, and may be connected to pump 130 via internal orexternal threads, a bolt or clamp flange, union connection, tubefitting, welds, or the like.

As seen in the exemplary embodiment illustrated in FIG. 3, pump 130 andcontrol valve assembly 135 may be in fluid communication with anactuator assembly 140 housed in drill bit 102 via one or more conduits137. Conduits 137 generally represent any form of fluid communicationdevice known to those of skill in the art, including, for example,hoses, pipe, or tubing. Actuator assembly 140, in one embodiment,generally represents a device capable of transforming the pressure orflow generated by pump 130 into a torque, or a moment for rotating eachof cutting elements 170. In at least one embodiment, actuator assembly140 converts hydraulic or pneumatic pressure generated by pump 130 intoa force that is used to rotate each of cutting elements 170. Forexample, as illustrated in FIGS. 4A and 4B, actuator assembly 140 maycomprise a housing 142 within which a piston 144 is positioned. Also,piston 144 may be mechanically coupled to a piston rod 148. As known inthe art, piston 144 is moveable within chamber 142 by generating apressure differential between chambers 143 and 145 via connections 137.As detailed above, such a pressure difference between chambers 143 and145 may be controlled by control valve assembly 135 coupled to pump 130.

According to certain embodiments, piston rod 148 of actuator assembly140 is mechanically coupled to a structural assembly 150. Generallyspeaking, structural assembly 150 couples piston rod 148 of actuatorassembly 140 with rotatable drive shaft 176, to apply torque tosubstrate 172 of cutting element 170. In the exemplary embodimentillustrated in FIGS. 4A and 4B, structural assembly 150 converts themotion of piston 144 and piston rod 148 into rotary motion (i.e.,torque) to rotate drive shaft 176. According to one exemplaryembodiment, structural assembly 150 comprises a rack 152 operablycoupled to a pinion 154. Rack 152 may be operably coupled to pinion 154in any number of ways and configurations. For example, as illustrated inthe side view of FIG. 4B, a plurality of gear-teeth 153 may be providedalong a portion of rack 152 which are engageable with a plurality ofcomplimentary-shaped gear-teeth 155 formed along the circumference ofpinion 154. Optionally, a biasing element 190 (e.g., a Belleville washerspring, a coil spring, etc.) may be positioned between the pinion 154and the bit body (e.g., bit blade 112) so that cutting element 170 isbiased toward cutting pocket 115. Of course, any rack-and-pinionconfiguration as known in the art may be employed, without limitation,for utilizing the motion of actuator assembly 140 to rotate rotatabledrive shaft 176. Pinion 154 and at least a portion of rack 152 may behoused within a recess 160 defined within blade 112 of drill bit 102,which may be optionally scaled and pressurized to inhibit exposure todrilling fluid or other environmental conditions.

In the exemplary embodiment illustrated in FIGS. 4A and 4B, piston rod148 is mechanically coupled to rack 152 via a pin 157 through piston rod148 and rack 152. Alternatively, piston rod 148 may be mechanicallycoupled to rack 152 via any number of other structural configurations,including, for example, a so-called “ball-and-socket” structure, ahinged structure, welding, threads, or other coupling configurations asknown in the art. In addition, although piston rod 148 is illustrated inFIGS. 4A and 4B as being mechanically coupled to rack 152, piston rod148 may be configured to rotate pinion 154 directly. For example, aplurality of gear-teeth may be provided along a portion of piston rod148 and configured to engage the plurality of complimentary gear-teeth155 formed along the circumference of pinion 154. In another embodiment,a portion of the substrate of a cutting element may include gear-teethand a rack may engage such gear-teeth directly.

In the exemplary embodiment illustrated in FIGS. 4A and 4B, pinion 154is mechanically coupled to rotatable drive shaft 176. Generallyspeaking, pinion 154 may be mechanically coupled to rotatable driveshaft 176 in any number of ways known to those of skill in the art,including, for example, by adhering, brazing, welding, or otherwisemechanically coupling substrate pinion 154 to drive shaft 176. Thus,movement of rack 152 and rotation of pinion 154 may convert the motionof piston 144 and piston rod 148 into rotary motion for rotating driveshaft 176 and cutting element 170. Accordingly, the exemplary embodimentillustrated in FIGS. 3, 4A, and 4B converts the energy or momentum ofdrilling fluids F into a force or moment (via motor 120, pump 130 andactuator assembly 140, for example) for applying torque to cuttingelement 170 to rotate the same relative to drill bit 102. During use, aselected magnitude of torque generated and applied to cutting element170 may be sufficient to rotate the cutting element 170 while performinga cutting operation (e.g., a drilling operation on a subterraneanformation). Further, as mentioned above, cutting element 170 may beconfigured to rotate through a selected angle so that a selected portionof a cutting edge may be used for cutting a subterranean formation.

Although illustrated as comprising a rack 152 operably coupled to apinion 154, structural assembly 150 may also comprise any number ofother structural configurations and/or devices capable of transformingthe motion of actuator assembly 140 to rotate shaft 176. For example,structural assembly 150 may comprise a cam mechanism (such as a camfollower assembly), a clutch assembly (such as a Sprag clutch assembly),a freewheel, a ratchet, a transmission or the like. Furthermore,actuator assembly 140 may comprise any device configured to provide asuitable motion for rotating (via structural assembly) shaft 176. Forexample, actuator assembly 140 may comprise a solenoid or any otheractuator as know in the art.

Additionally and optionally, as shown in FIG. 4A, separation element 165(e.g., a washer or other element) may be positioned between a frontsurface of cutting pocket 115 and a back surface of substrate 172 ofcutting element 170. Separation element 165 may comprise a washer or alayer of material, such as a metal or ceramic shim. In anotherembodiment, separation element 165 may be configured to reduce frictionand/or wear between cutting element 170 and cutting pocket 115. In afurther embodiment, separation element 165 may be sacrificial (i.e., maybe softer than substrate 172 of cutting element 120 and/or cuttingpocket 115). In another embodiment, a coating, such as diamond, siliconcarbide, chrome, etc., may be formed (e.g., electroplated, thermallysprayed, sputtered, electrolessly deposited, or otherwise formed ordeposited) upon at least one of cutting pocket 115 and substrate 172.Such a configuration may facilitate rotation of cutting element withrespect to cutting pocket 115.

In a farther embodiment, a push rod or other structural member maydirectly engage a feature formed in the substrate of a cutting elementto apply torque to the substrate for rotating the cutting element. Forexample, FIG. 4C shows an actuator assembly 140 and a push rod 187configured for engaging the engaging features 188 formed into asubstrate 172 of cutting element 170. More particularly, an end 189 ofpush rod 187 may be structured for interacting with engaging features188 (e.g., a surface or other aspect of a recess) to rotate cuttingelement 170. Thus, it may be understood that actuator assembly 140 maycause push rod 187 to reciprocate (i.e., toward and away) with respectto substrate 172. More particularly, as shown in FIG. 4D, push rod 187may reciprocate along a direction labeled “d.” Also, optionally, asshown in FIG. 4D, push rod 187 may be flexible and may be biased (e.g.,bent or otherwise biased) toward engaging features 188 formed insubstrate 172. Such a configuration may cause the push rod 187 to lockinto an appropriately positioned engagement feature 188.

FIG. 5 is a schematic, side cross-sectional view of an alternativeembodiment of a rotary drill bit employing an actuator assembly forapplying torque to a rotatable cutting element. As illustrated in thisexemplary embodiment, a drilling apparatus may comprise a motor 220 forpowering a power source 230. In at least one embodiment, motor 220 maybe a positive displacement motor for converting the momentum or energyof drilling fluids F flowing through a bore in a drill string intomechanical energy, as known in the art. Thus, motor 220 may convert theflow of drilling fluids F into mechanical energy to rotate output shaft225 coupled to power source 230 (e.g., an electrical generator, ahydraulic pump, etc.). Alternatively, motor 220 may comprise any otherconfiguration or motor capable of driving power source 230, including,for example, a Moineau-type motor, a turbine-type motor, or the like.Furthermore, the present invention contemplates an individual rotationdevice or mechanism may be coupled to each of cutting elements 270. Forexample, a miniature hydraulic motor may be mechanically coupled to eachcutting element 270. Such a configuration may eliminate the need forstructural assembly 150. Thus, in at least one embodiment, power source230 is configured to convert the mechanical energy generated by motor220 into hydraulic energy or electricity for powering atorque-generating assembly, such as actuator assembly 240 or 340(illustrated in FIGS. 6 and 7, respectively). Generally, in oneembodiment, power source 230 may comprise any form of device capable ofgenerating electricity, as known in the art. As seen in the exemplaryembodiment illustrated in FIG. 5, power source 230 may be incommunication with an actuator assembly (e.g., actuator assembly 240and/or 340, as discussed below) via one or more connections 235.Connections 235 generally represent any form of electrical conduit knownto those of skill in the art, including, for example, electrical cables,wiring, or the like.

More particularly, FIG. 6 shows an enlarged cross-sectional view of anembodiment of an actuator assembly 240 for applying torque to arotatable cutting element. Actuator assembly 240 generally represents adevice capable of transforming electricity or hydraulic energy generatedand supplied by power source 230 into torque for rotating cuttingelement 270. In at least one embodiment, actuator assembly 240 comprisesa motor (e.g., an electric motor or a hydraulic motor) that converts theelectricity or hydraulic energy generated and supplied by power source230 into torque. For example, FIG. 6 shows an actuator assembly 240comprising a relatively compact motor (such as, for example, anelectrically-powered geared motor or stepper motor) configured togenerate and apply torque to a drive shaft 276 coupled to a substrate272 of cutting element 270. Optionally, the torque and speed of rotationof drive shaft 276 relative to the torque and speed of rotationgenerated by actuator assembly 240 may be controlled by a transmission255 coupled to actuator assembly 240. Generally, transmission 255 mayrepresent a gearbox or other device and may be desirable for convertingan unsuitably high speed and low torque generated by an actuatorassembly 240 (e.g., an electrically-powered motor) to a lower speed withhigher torque, or vice versa.

Similar to the exemplary embodiment illustrated in FIG. 4A, actuatorassembly 240 may be housed within recess 260 defined within a blade 212of a drill bit. Also, optionally, a biasing element 190 (e.g., aBelleville washer spring, a coil spring, etc.) may be positioned betweenthe actuator assembly 240 and the bit body (e.g., bit blade 212) so thatcutting element 270 is biased toward cutting pocket 215. Recess 260 may,optionally, be sealed and pressurized to protect actuator 240 fromexcessive exposure to drilling fluids. As with cutting element 170,cutting element 270 generally represents any form of cutting elementcapable of cutting a subterranean formation, and is generally comprisedof a structure and materials similar or identical to those of cuttingelement 170. In addition, drive shaft 276 may be mechanically coupled tosubstrate 272 of cutting element 270 in accordance with any of theabove-described embodiments. Also, cutting element 270 may be rotatablymounted within a cutting pocket 215 defined in bit blade 212 of a drillbit. Cutting pocket 215 of bit blade 212 may be generally configuredsimilar to cutting pocket 115 to surround at least a portion of aperiphery of cutting element 270 when positioned within cutting pocket215. In addition, as explained above, a separation element 265 (e.g., awasher element or the like) may be positioned between front surface ofcutting pocket 215 and a back surface of substrate 272 of cuttingelement 270.

FIG. 7 is an enlarged cross-sectional view of an additional embodimentof an actuator assembly for rotating a cutting element. Particularly,actuator assembly 340 generally represents a device capable oftransforming energy (e.g., hydraulic energy or electricity) generatedand supplied by a device (e.g., a pump, a generator, or the like) intolinear motion for rotating cutting elements 370. In at least oneembodiment, actuator assembly 340 may be configured to move a piston rodvia electricity generated and supplied by a generator (such as powersource 230) via connection 335. For example, actuator assembly 340 maycomprise a solenoid or any other device for moving column 341 and may beelectrically powered, as known in the art. In another embodiment,actuator assembly 340 may comprise a reciprocating actuator having acolumn 341 coupled to a piston rod 343 configured to drive a camassembly 355 coupled to a drive shaft 376 and may be hydraulicallypowered. Optionally, a biasing element 190 (e.g., a Belleville washerspring, a coil spring, etc.) may be positioned between the actuatorassembly 340 and the bit body (e.g., bit blade 312) so that cuttingelement 370 is biased toward cutting pocket 315. Cam assembly 355generally represents any form of cam mechanism (such as a cam indexerassembly or a earn follower assembly) capable of converting the linearmotion generated by actuator assembly 340 into rotary motion forrotating drive shaft 376. Cutting element 370 generally represents anyform of cutting element capable of cutting a formation, and is generallycomprised of a structure and materials similar or identical to that ofcutting element 170. In addition, drive shaft 376 may be mechanicallycoupled to a substrate 372 of cutting element 370 in accordance with anyof the above-described manners of mechanically coupling drive shaft 176to cutting element 170. Further, a separation element 365 may bepositioned between the cutting pocket 315 of bit blade 312 and thecutting element 370.

Although actuator assemblies 140, 240, and 340 have been described andillustrated as including hydraulic assemblies, electric motors, and camindex assemblies, respectively, these actuator assemblies may compriseany form of assembly or device capable of generating torque for rotatinga cutting element, as known in the art. For example, actuator assemblies140, 240, and 340 may comprise pneumatic motors or pumps, gas-poweredmotors or pumps, induction motors or pumps, and the like. Suchassemblies may include any number of devices, including, for example,fluid-driven motors, turbines, batteries, fuel cells, and the like. Themechanical motion generated by such assemblies may be either rotational,linear, or combinations thereof as desired. These mechanical forces ormotions may then be transmitted to a rotatable cutting element by cammechanisms, clutches, freewheels, ratchets, transmissions or the like.

In at least one embodiment, torque may be constantly generated andapplied by a plurality of actuator assemblies 140, 240, and 340 to aplurality of drive shafts 176, 276, and 376 respectively affixed toplurality of cutting elements 170, 270, and 370. Alternatively, theseactuator assemblies 140, 240, and 340 may be controlled periodicallyand, optionally, may generate individually and apply torque to each ofthe drive shafts affixed to each of a plurality of cutting elements,respectively. In other words, the above-described actuator assembliesmay be used to constantly and continuously rotate a cutting element, ormay be used to periodically index a cutting element, as needed. As willbe understood by those of skill in the art, constant torque may berequired in relatively demanding environments, while periodic indexationmay suffice when in less demanding conditions, resulting in significantpower conservation.

FIG. 8A is a schematic, side cross-sectional view of an exemplaryembodiment of a drill bit 301 including a sleeve assembly 303 forapplying torque to at least one cutting element 370. FIG. 8B is aperspective view of a cam assembly 384 employed by the sleeve assembly303 illustrated in FIG. 8A. FIG. 8C is a side view of cam assembly 384illustrated in FIG. 8B. According to the embodiments illustrated inthese figures, an exemplary sleeve assembly for applying torque to acutting element may comprise a cam follower 386 positioned adjacent to acam assembly 384, wherein the cam assembly 384 is mounted to a sleeve382. In at least one embodiment, sleeve 382 exhibits a substantiallyannular or ring-like shape and may be configured to be rotatablypositioned within an annular recess 381 defined generally along theouter circumference or gage portion of a drill bit body 380. Sleeve 382may be formed of any number of materials or structures known to those ofthe art, including, for example, tungsten carbide or steel. According tocertain embodiments, annular recess 381 defined along the outercircumference or gage portion of drill bit body 380 is formed tosubstantially embody the inverse of at least a portion of sleeve 382.

As seen in FIG. 8A, one or more radial bearing assemblies 390 may beprovided between the inner circumferential surface of sleeve 382 and theouter circumferential surface of recess 381 in drill bit body 380.Generally, radial bearing assemblies 390 may be annularly-shaped andconfigured to allow sleeve 382 to rotate within recess 381 of drill bitbody 380 despite radial loads experienced during subterranean drilling.Radial bearing assemblies 390 generally represent any form of bearingassembly capable of withstanding radial loads, including, for example,polycrystalline diamond bearings (e.g., PDC bearings), radial roller orball bearings, deep-groove bearings, filling notch bearings, and thelike. Similarly, one or more thrust bearing assemblies 392 may beprovided between the upper and lower surfaces of sleeve 382 and theinner surfaces of recess 381. Generally, thrust bearing assemblies 392are annularly-shaped and configured to allow sleeve 382 to rotate withinrecess 381 of drill bit body 380 despite the axial loads experiencedduring subterranean drilling. Thrust bearing assemblies 392 generallyrepresent any form of bearing assembly capable of withstanding axialloads, including, for example, polycrystalline diamond thrust bearings,ball thrust bearings, roller thrust bearings, tapered roller bearings,and the like. Radial bearing assemblies 390 and thrust bearingassemblies 392 may be, optionally, lubricated by drilling fluids pumpedthrough drill bit 301.

In the exemplary embodiment illustrated in FIG. 8A, cam assembly 384 ismounted on the upper surface of the inner circumference of sleeve 382.As seen in the exemplary embodiment of FIG. 8B, the body of cam assembly384 may be formed in a substantially annular shape and may include aplurality of cam inserts 385. In at least one embodiment, each caminsert 385 is formed to have a height that differs slightly from itscircumferentially adjacent inserts. For example, as seen in the sideview of FIG. 8C, each insert 385 in cam assembly 384 may be formed tohave a height that exceeds or differs from circumferentially adjacentinserts, resulting in an undulating cam surface. A superhard material,such as polycrystalline diamond, may be disposed on the upper surface ofeach insert 385 in cam assembly 384. Of course, generally, inserts 385may each exhibit a height so that the cam surface of cam assembly 384causes cam follower 386 to move in a desired manner.

As illustrated in FIG. 8A, cam follower 386 may be housed in drill bit380 directly above rotating cam assembly 384. In at least oneembodiment, cam follower 386 comprises a push rod 388 housed inside arecess formed in the body of drill bit 380 and attached to cam follower386. Biasing element 387 may comprise a spring or similar structure forbiasing push rod 388 in a direction toward cam assembly 384. In at leastone embodiment, one end of push rod 388 is mechanically coupled tocutting element 370, while a tracing tip 389 is formed on follower 386.Thus, such a configuration may be configured to trace or follow thegenerally undulating upper surface of cam assembly 384 according to theconfiguration of inserts 385. Tracing tip 389 may be formed of anynumber of materials, including, for example, a superhard material suchas polycrystalline diamond.

As seen in FIG. 8A, in at least one embodiment, a formation engagingportion 394 is formed along at least a portion of the outercircumferential surface of rotating sleeve 382. For example, formationengaging portion 394 may be formed to extend beyond recess 381 and theexterior gage surface “G” of drill bit 380 by a distance W. In theexemplary embodiment illustrated in FIG. 8A, formation engaging portion394 is configured to contact at least a portion of a bore drilled in asubterranean formation. During an exemplary drilling operation, as drillbit 380 is rotated about its axis by a motor within a borehole drilledin a subterranean formation, formation engaging portion 394, which mayextend beyond the outer circumferential surface of drill bit 380 bydistance W, may contact at least a portion of an inner surface of theborehole. The present invention further contemplates that attributes ofthe surface, labeled “S,” of formation engaging portion 394 may betailored for “aggressiveness.” Put another way, surface S may includegage cutting elements or structures (e.g., natural diamonds, PDCcutters, tungsten carbide elements, or other materials) that mayinfluence that degree to which surface S engages or resists slidingcontact with a subterranean formation. The resulting force from contactwith the inner surfaces of the borehole may cause rotating sleeve 382,and cam assembly 384 mounted thereon, to rotate with respect to the mainbody of drill bit 380. As rotating sleeve 382 and cam assembly 384rotate relative to drill bit 380, tracing tip 389 of cam follower 386follows the generally undulating upper surface of cam assembly 384comprised of inserts 385. Thus, push rod 388 (biased by resilient member387 and connected to tracing tip 389) may be lowered or raised inaccordance with the height of each insert 385, resulting in a generallycyclic motion. This resulting cyclic motion by push rod 388 may then beused to rotate cutting element 370 coupled thereto.

Push rod 388 may be coupled to cutting element 370 using any number ofconfigurations or structural assemblies. For example, in at least oneembodiment push rod 388 is coupled to cutting element 370 by astructural assembly (such as structural assembly 150, illustrated inFIGS. 4A-4B) comprising a rack-and-pinion assembly for converting thelinear reciprocating motion of push rod 388 into rotary motion forrotating a drive shaft affixed to cutting element 370. However, as willbe appreciated by those of skill in the art, push rod 388 may also becoupled to cutting element 370 using any number of other structuralconfigurations and/or devices capable of using the linear motion of pushrod 388 to rotate cutting element 370.

Thus, a torque may be generated and applied to a cutting element byutilizing the rotary motion of a rotary drill bit, without the need foradditional torque-generating assemblies. As will be appreciated, drillbit 380 may comprise any number of earth-boring or drilling tools asknown in the art, including without limitation, for example, core bits,roller-cone bits, fixed-cutter bits, eccentric bits, bicenter bits,reamers, reamer wings, and the like. The present invention alsocontemplates methods for operation of a drill bit 380 as describedabove. For example, during drilling with a drill bit 380, it may beadvantageous to stop movement (rate-of-penetration) and rotate the drillbit 380 to cause interaction between the subterranean formation and theformation engaging portion 394 of the drill bit 380. In this way, atleast one cutting element configured to rotate may be indexed (i.e.,rotated). It may be appreciated that such rotation may cause so-called“bit whirl,” which may cause a formation engaging portion 394 to rotateeven if it is not otherwise intended to rotate or, for some otherreason, does not rotate during drilling (e.g., the formation engagingportion 394, in one embodiment, may not be designed to contact thesubterranean formation during drilling). Summarizing, ceasingrate-of-penetration and rotating a drill bit including a formationengaging portion 394 so that at least one cutting element rotates duringsuch rotation of the drill bit is contemplated by the present invention.

Although actuator assemblies 140, 240 and 340 and cam follower 386 areillustrated in FIGS. 3, 6, 7, and 8A, respectively, as being coupled toeach of the cutting elements disposed on a drill bit, in many situationsit may prove both difficult and impractical to apply torque to each andevery cutting element disposed on a drill bit. Generally, the presentinvention contemplates that a drill bit may include at least one cuttingelement that is rotatable by an application of force or torque to thecutting element. Accordingly, in another embodiment, torque may beapplied to a plurality of selected cutting elements disposed on a drillbit. For example, torque may only be applied to a plurality of selectedcutting elements having the highest work rate, or to those cuttingelements that are otherwise highly taxed during the drilling process, asneeded. In many embodiments, the cutting elements having the highestwork rate are those positioned generally near the nose or generally nearthe shoulder of a drill bit. For example, on an 8.5 inch diameter drillbit having 35 cutters formed on 4-5 blades, it may only be necessary toapply torque to 12-15 of the cutting elements disposed on the drill bit.Although torque is only applied to a portion of the cutting elementsdisposed on such an exemplary drill bit, substantial performance gainsrealized by applying torque to each cutting element disposed on a drillbit (as described below in connection with FIG. 8) are also realizedwhen torque is only applied to those cutting elements having the highestwork rate. This selective application of torque to the various cuttingelements disposed on a drill bit may thus realize various gains inenergy efficiency and simplicity without significant losses in cuttingelement performance.

It should also be appreciated that any of the above-describedembodiments may be implemented with respect to a cutting element usedfor a machining or other cutting operation. For example, a cuttingelement may be rotated in a machining operation by coupling the cuttingelement to an output shaft of an electric motor and energizing the motorwhile machining a material with the cutting element. In addition, it maybe appreciated that such a configuration may allow for largertorque-generation apparatuses, since available space may be more amplethat within a rotary drill bit.

FIG. 9 is a chart illustrating the advantages of applying torque to acutting element. More specifically, FIG. 9 illustrates the vertical orweight-on-bit force versus the linear distance traveled for a cuttingelement cutting Sierra White granite, as obtained using a cuttingelement evaluation machine configured to force a cutting element througha selected material at a selected depth-of-cut. Further, the data shownin FIG. 9 was produced by forcing a PDC cutter through Sierra Whitegranite while rotating the PDC cutter. More specifically, an electricmotor was coupled to a shaft, which was attached to the substrate of aPDC cutter. The electric motor was energized and rotated at a speed ofabout 5 revolutions per minute while the cutting element was forced (ata selected depth of cut, for example, 0.110 inches) through the SierraWhite granite. As evidenced by FIG. 9, cutting elements that are brazedwith a cutting pocket (either chamfered or non-chamfered) and cuttingelements that are merely free to rotate due to contact with the materialbeing cut exhibit a much shorter lifespan and are not able to functionas efficiently as cutting elements that are rotated by application of atorque to the cutting element during cutting (such as cutting elementsrotated by a torque-generating member). For example, as seen in FIG. 9,the brazed chamfered or non-chamfered cutting elements that are free torotate during cutting were destroyed after only having removedapproximately 10,000 ft of Sierra White granite. However, a cuttingelement to which a torque of sufficient magnitude to rotate the cuttingelement during cutting continued to operate well after having removedover 14,000 ft of Sierra White granite. This so-called“actively-rotated” cutting element thus lasted much longer and exhibitedmuch lower vertical force values than brazed cutting elements or cuttingelements that were merely free to rotate.

Accordingly, applying torque to at least one cutting element coupled toa drill bit or at least one cutting element coupled to equipment formachining (e.g., a lathe, a so-called planer, or other machinery forcutting materials) may significantly prolong the life of such at leastone cutting element. Advantageously, this configuration may also keepthe engagement point between the subterranean formation being drilledand the cutting element much cooler since new portions of the cuttingelement's circumference are continually rotating into the cutting edge.Such a configuration may also advantageously keep the cutting edge ofthe cutting element much sharper than conventional cutting elements,resulting in increased cutting efficiency. For example, a drill bit mayexhibit a higher rate of penetration for a given weight-on-bit, ascompared to a conventional drill bit. Potentially, such a configurationmay enable the drilling of various subterranean formations that have notbeen previously drillable by drill bits employing conventional cuttingelements.

FIG. 10 is an enlarged view of a rotatable cutting element having anexemplary impelling feature for impelling debris generated by thecutting element. In at least one embodiment, cutting element 470comprises a table 474 formed on a substrate 472. As with cutting element170, cutting element 470 generally represents any form of cuttingelement capable of cutting a formation, and is generally comprised of astructure and materials similar or identical to that of cutting element170. A drive shaft 476 may be mechanically coupled to substrate 472 ofcutting element 470 in accordance with any of the above-describedmanners of mechanically coupling drive shaft 176 to cutting element 170.In general, drive shaft 476 affixed to substrate 472 of cutting element470 is configured so as to be rotated by a torque-generating member. Forexample, drive shaft 476 affixed to substrate 472 of cutting element 470may be attached to any of the actuator assemblies or cam assembliespreviously described. As with cutting element 170, cutting element 470may optionally be rotatably mounted within a cutting pocket 415 definedin bit blade 412 of a drill bit. Cutting pocket 415 of bit blade 412 maybe configured similar to cutting pocket 115, as described above.

According to the exemplary embodiment illustrated in FIG. 10, at leastone impelling feature 480 comprises at least one groove formed into atleast a portion of an exterior surface of substrate 472. In anotherembodiment impelling feature 480 may comprise at least one protrusionformed upon at least a portion of the exterior surface of substrate 472.Impelling feature 480 may be formed in a substantially helical shape.Impelling feature 480 may be formed in the exterior surface of substrate472 in accordance with any number of processes or techniques. Forexample, a grinding device may be used to form a groove into at least aportion of an exterior surface of substrate 472 formed of a materialsuch as tungsten carbide. In another example, hard-facing may be appliedto at least a portion of an exterior surface of the substrate 472 toform a protrusion. Alternatively, a mold embodying the inverse of thetopographical features (such as a helical groove or protrusion) of adesired substrate may be prepared. As will be appreciated by those ofskill in the art, impelling feature 480 may be formed to have any numberof sizes, widths, and shapes.

As cutting element 470 is rotated by a torque-generating member whiledrilling a subterranean formation, debris 485 generated by this drillingoperation may be channeled or impelled by impelling feature 480 awayfrom and out of cutting pocket 415. Specifically, impelling feature 480formed along the exterior surface of substrate 472 of cutting element470 may clear drilling debris 485 from cutting pocket 415 (e.g., similarto an auger). By clearing debris 485 from cutting pocket 415, impellingfeature 480 may allow cutting element 470 to freely rotate withincutting pocket 415. Such uninhibited rotation may allow cutting element470 to maintain a substantially constant rotation speed and torquewithin cutting pocket 415, resulting in an efficient cutting of thesubterranean formation being drilled.

FIGS. 11A and 11B are side and top views, respectively, of an exemplarydrilling system according to at least one additional embodiment. As seenin these figures, exemplary drilling system 500 may comprise a drill bit502 threaded onto, coupled or attached to a drill string 506. Drill bit502 may represent any type of earth-boring or drilling tool; including,for example, core bits, roller-cone bits, fixed-cutter bits, eccentricbits, bicenter bits, reamers, reamer wings, and the like. Drill bit 502may also be formed in any number of ways and of any type of material orcombination or materials. For example, drill bit 502 may be machinedfrom steel or may be manufactured by infiltrating a binder into atungsten carbide particulate, as described above.

In at least one embodiment, one or more rotatable cutting elements 570and/or one or more fixed (i.e., stationary) cutting elements 571 may bemounted to the face or blades of bit body 510 of drill bit 502.Generally speaking, cutting elements 570 and 571 may comprise anycutting element capable of cutting a subterranean formation; including,for example, PDC or other superabrasive cutters. Cutting elements 570and 571 may also be formed in any number of configurations and of anymaterial or combination of materials. For example, in certainembodiments (and as illustrated in FIG. 12A), cutting element 570 maycomprise a superabrasive layer or table 574 bonded to or formed upon asubstrate 572. As known in the art, a “superabrasive material,” as usedherein, may refer to a material exhibiting a hardness exceeding ahardness of tungsten carbide. Optionally, and as with all previousembodiments (namely; cutting elements 170, 270, and 370), cuttingelements 570 may comprise a unitary or integrally formed structurecomprising, for example, diamond, silicon carbide, boron nitride, or acombination of the foregoing.

FIG. 12A shows a partial, enlarged view of cutting element 570 withindrill bit 502 and depicts at least one embodiment of a mechanism forrotating cutting element 570. As with previous embodiments, table 574 inFIG. 12A may be formed of any material or combination of materials usedfor cutting formations; including, for example, a superhard orsuperabrasive material such as polycrystalline diamond. Similarly,substrate 572 may comprise any material or combination of materialscapable of adequately supporting a superabrasive material duringdrilling of a subterranean formation; including, for example, cementedtungsten carbide. For example, cutting element 570 may comprise a table574 comprising polycrystalline diamond bonded to a substrate 572comprising cobalt-cemented tungsten carbide. In addition, optionally, asexplained above, after formation of table 574, a catalyst material(e.g., cobalt, nickel, etc.) may be at least partially removed (e.g., byacid-leaching) from table 574.

Cutting element 570 may be rotatably mounted to bit body 510 of drillbit 502 in any number of ways and configurations. For example, cuttingelement 570 may be rotatably mounted to drill bit 502 by adhering,brazing, threadedly affixing, welding, or securing cutting element 570to a first end of a coupling structure 576. Coupling structure 576generally represents any structure capable of coupling cutting element570 to the bit body 510 (e.g., the face or blades of body 510) of drillbit 502. In at least one embodiment, coupling structure 576 may comprisea second end 577 that is larger than an aperture 517 defined in drillbit 502 to effectively retain cutting element 570 within a cuttingpocket 515 defined in bit body 510 of drill bit 502. Cutting pocket 515may comprise a recessed space or aperture open to an outside portion ofbit 502. A biasing element 590 (e.g., a Belleville washer spring, a coilspring, etc.) may also be positioned between the second end 577 ofcoupling structure 576 and the bit body 510 of bit 502 to bias cuttingelement 570 toward cutting pocket 515. Optionally, cutting element 570may be rotatably mounted to drill bit 502 in a manner similar to thatdisclosed in U.S. Pat. No. 4,553,615 to Grainger and/or U.S. patentapplication Ser. No. 11/148,806 to Cooley et al., the entirety of thedisclosure of each of which is hereby incorporated by this reference.

In certain embodiments, a separation element (such as separation element165 in FIG. 4A) may be positioned between cutting pocket 515 and cuttingelement 570. This separation element may be configured to reducefriction and/or wear between cutting element 570 and cutting pocket 515.In one embodiment, this separation element may be sacrificial (i.e., maybe softer than cutting element 570 and/or cutting pocket 515).Separation element 165 may comprise a washer or a layer of material,such as a metal, polymer, or ceramic shim. In another embodiment, acoating, such as diamond, silicon carbide, tungsten carbide, chrome,etc., may be formed (e.g., electroplated, thermally sprayed, sputtered,electrolessly deposited, or formed or deposited) upon at least one ofcutting pocket 515 and cutting element 570. In addition, at least one ofcutting pocket 515 and cutting element 570 may be coated in the mannerdetailed in U.S. Provisional Application No. 60/850,969, the entirety ofthe disclosure of which is hereby incorporated by this reference. Such aconfiguration may facilitate rotation of cutting element 570 withrespect to cutting pocket 515.

As with previous embodiments, cutting element 570 may rotate in responseto torque applied to cutting element 570 by a torque-generatingassembly. In at least one embodiment, cutting element 570 may rotatewithin an angle of rotation of less than 360 degrees, or in other words,cutting element 570 may rotate less then one full turn in response totorque from a torque-generating assembly. In certain embodiments, thistorque-generating assembly may comprise a cam assembly 580 coupled todrill string 506 (which may comprise a motor), a cam follower assembly590 in contact with or coupled to cam assembly 580, and atorque-applying structure 560 configured to transmit force from camassembly 580 to generate torque on cutting element 570, as illustratedin FIG. 11A.

Cam assembly 580, which may be formed in any shape or size and of anymaterial or combination of materials, generally represents any type orform of cam mechanism or structure. For example, as illustrated in FIGS.13A-13D, cam assembly 580 may comprise a substantially annular-shapedcam body 582 having a cam surface 581. Cam surface 581 of cam body 582may be formed in any shape or size. For example, cam surface 581 may bea planar surface that is angled, tapered, or inclined with respect todrill string 506. In certain embodiments, cam surface 581 may be formedof a single, unitary structure or material. In an additional embodiment,cam surface 581 may comprise the collective surfaces of a plurality ofcam inserts 584 affixed to cam body 582, as illustrated in FIGS.13A-13D.

Cam inserts 584 may be formed in any shape or size and of any materialor combination of materials. For example, as illustrated in FIG. 13B,cam inserts 584 may each comprise a superabrasive layer or table 585bonded to or formed upon a substrate 583. In an additional embodimentcam inserts 584 may each comprise a unitary or integrally formedsuperabrasive structure comprising, for example, diamond, boron nitride,silicon carbide, or a combination of the foregoing.

As with previous embodiments, table 585 in FIG. 13B may be formed of anymaterial or combination of materials; including, for example, asuperhard or superabrasive material such as polycrystalline diamond,silicon carbide, boron nitride, diamond, or any superabrasive material.Similarly, substrate 583 may comprise any material or combination ofmaterials capable of adequately supporting a superabrasive material;including, for example, cemented tungsten carbide. For example, caminsert 584 may comprise a table 585 comprising polycrystalline diamondbonded to a substrate 583 comprising cobalt-cemented tungsten carbide.In addition, as explained above, after formation of table 585, acatalyst material (e.g., cobalt, nickel, etc.) may be at least partiallyremoved (e.g., by acid-leaching) from table 583.

As seen in FIGS. 13A-13D, each cam insert 584 may be structured andpositioned proximate to an adjacent cam insert 584 to form cam surface581. In certain embodiments, each cam insert 584 may abut and/orpartially surround a circumferentially adjacent cam insert 584. Forexample, as illustrated in FIG. 13B, a recess 586 may be defined along aportion of the circumference of each cam insert 584. As illustrated inFIG. 13A, this recess 586 may be sized to receive at least a portion ofan adjacent cam insert 584 to substantially reduce any gaps betweenadjacent cam inserts 584, which may result in cam surface 581 beingsubstantially continuous and smooth.

In at least one embodiment, each cam insert 584 may be formed to have aheight that differs slightly from its circumferentially adjacentinserts, resulting in a generally planar or undulating cam surface (suchas the undulating cam surface illustrated in FIG. 8C). In an additionalembodiment, each cam insert 584 of cam assembly 580 may be substantiallythe same size and shape. For example, as illustrated in FIG. 13C, aplurality of substantially identical cam inserts 584 havingsubstantially identical heights may be affixed to a cam body 582comprising a substantially planar bottom surface 587 and a substantiallyplanar top surface 589. In this exemplary embodiment, each cam insert584 may be positioned and affixed within an insert pocket 588 defined incam body 582. Insert pockets 588 may be defined in any shape and sizeand to any desired depth. In at least one embodiment, the depth of eachinsert pocket 588 defined in the top surface 589 of cam body 582 mayvary. For example, as illustrated in FIG. 13C, the depth d₁ of a firstinsert pocket 588 may be substantially less than the depth d₂ of asecond insert pocket 588. In an additional embodiment, the depth of eachinsert pocket 588 defined in the top surface 589 of cam body 582 may besubstantially identical.

FIGS. 14A-14C are top, side, and perspective views, respectively, of anexemplary cam follower assembly 590 according to at least oneembodiment. Cam follower assembly 590 generally represents any type orform of structure or assembly for contacting, tracing, or following thecam surface 581 of cam assembly 580. Cam follower assembly 590 may beformed in any shape or size and of any material or combination ofmaterials. For example, as illustrated in FIGS. 14A-14C, cam followerassembly 590 may comprise a plurality of cam follower elements 594, eachof which may exhibit a selected shape and size and may comprise anyselected material or materials. For example, in at least one embodiment,each cam follower element 594 may comprise a table 595 of superhard orsuperabrasive material (such as polycrystalline diamond, boron nitride,silicon carbide, etc.) bonded to a substrate 593 (comprising, forexample, cemented tungsten carbide). Optionally, cam follower elements594 may comprise a unitary or integrally formed structure comprising,for example, diamond, silicon carbide, boron nitride, or a combinationof the foregoing.

In at least one embodiment, each of the cam follower elements 594 in camfollower assembly 590 may be connected or attached to one another by aconnecting structure 592. Connecting structure 592 generally representsany type or form of structure or assembly for connecting or attachingeach cam follower element 594 in cam follower assembly 590. Connectingstructure 592 may be formed in any shape or size and of any material orcombination of materials; including, for example, metal (e.g., tungstencarbide, steel, etc.). Optionally, as shown in FIGS. 14A and 14B,connecting structure 592 may generally resemble a plate or ring. In atleast one embodiment, each earn follower element 594 may be adhered,brazed, welded, press-fit, or affixed to connecting structure 592. In anadditional embodiment, as illustrated in FIGS. 14A and 14C, each camfollower element 594 may be disposed or captured within a recess 599defined in connecting structure 592. In certain embodiments, recess 599may be larger than cam element 594 to allow cam follower element 594 toat least partially move or shift within recess 599. As illustrated inFIGS. 14A and 14C, a portion of connecting structure 592 also may bedisposed within a recess 597 defined within each cam follower element594.

In certain embodiments, each cam follower element 594 may be connected,attached, affixed, in contact with, or coupled to a torque-applyingstructure. For example, as illustrated in FIGS. 14A and 14C, a recess596 defined in the top surface of each cam follower element 594 may bestructured or defined so as to receive or couple to a portion of atorque-applying assembly. Recess 596 may be formed in any shape or size.For example, as seen in FIGS. 14A, 14C, 15A, and 15B, recess 596 may begenerally hemispherical in shape or curved, rounded, radiused, orconcave.

In at least one embodiment, and as illustrated in FIGS. 11A, 15A, and15B, recess 596 of cam follower element 594 may be structured to receiveor couple to a first end 562 of a torque-applying structure 560.Torque-applying structure 560 generally represents any type or form ofstructure or assembly capable of applying torque to at least a portionof cutting element 570. For example, in the exemplary embodimentsillustrated in FIGS. 11A-12C, 15A, and 15B, and as described in greaterdetail below, torque-applying structure 560 may be a push rod structuredto apply a force generated by a torque-generating assembly (comprising,for example, rotary drill bit 502, cam assembly 580, and/or cam followerassembly 590 as discussed in detail below) to cutting element 570, whichmay result in torque being applied to cutting element 570. In theseexemplary embodiments, and as illustrated in FIGS. 12A-12C,torque-applying structure 560 may comprise a first end 562 and a secondend 564. First end 562 and second end 564 of torque-applying structure560 may exhibit selected shapes, sizes and material(s), withoutlimitation. For example, as illustrated in FIGS. 12A-B, 15A, and 15B,first end 562 of torque-applying structure 560 may be generally rounded,domed, or otherwise shaped. In addition, in at least one embodiment,first end 562 may comprise a superhard or superabrasive material havinga rounded or ovoid end surface 565 (such as polycrystalline diamond)bonded to a substrate 563 (comprising, for example, cemented tungstencarbide). In an additional embodiment, first end 562 may comprise aunitary or integrally formed structure comprising, for example, diamond,boron nitride, and/or silicon carbide.

In certain embodiments, first end 562 of torque-applying structure 560may be attached, affixed, connected, coupled to, in contact with, orconfigured to interact with a portion of cam follower assembly 590. Forexample, as illustrated in FIGS. 11A, 15A, and 15B, first end 562 oftorque-applying structure 560 may be positioned generally within therecess 596 defined cam follower element 594. Further, and as illustratedin FIGS. 11A-12B, second end 564 of torque-applying structure 560 may becoupled to, biased against, mechanically engaged with, or in contactwith a portion of cutting element 570.

As detailed above, second end 564 of torque-applying structure 560 maybe formed in any shape or size and of any material or combination ormaterials. For example, second end 564 may be structured to abutagainst, engage, or be received by engaging features 575 of cuttingelement 570. As with previous embodiments, engaging features 575 may beany structure capable of engaging, receiving, contacting, or interactingwith an opposing structure. Examples of engaging features 575 include,without limitation, recesses, protuberances, gear teeth, or any othersuitable structure or aperture.

As detailed above, torque-applying structure 560 may comprise anymaterial or combination of materials. For example, as illustrated inFIG. 12C, torque-applying structure 560 may comprise a flexible portion567 and a substantially rigid portion 569. In certain embodiments,flexible portion 567 may bend or flex while applying torque to cuttingelement 570, while rigid portion 569 may exhibit limited or nodeformation. In addition, portions of torque-applying structure 560 mayexhibit an alternate selected flexibility. For example, a centralportion of torque-applying structure 560 may exhibit limited or nodeformation, while an end portion of torque-applying structure 560 maybend or flex while applying torque to cutting element 570.Torque-applying structure 560 may also be attached, connected, disposedwithin, or coupled to bit body 510 of rotary bit 502. For example, asillustrated FIGS. 11A and 12A, torque-applying structure 560 may bedisposed within a passageway 519 defined in bit body 510 of rotary bit502. As illustrated in FIG. 12A, optionally, torque-applying structure560 may also comprise a bushing member 566 positioned between theinterior of bit body 510 and torque-applying structure 560. Such aconfiguration may be structured to reduce friction between bit body 510and torque-applying structure 560.

In at least one embodiment, rotary drill bit 502 may be structured torotate relative to, and substantially independent of, drill string 506(and cam assembly 580 coupled thereto). Accordingly, becausetorque-applying structure 560 may be disposed within or coupled to bitbody 510 of bit 502, torque-applying structure 560 may also rotate, inconjunction with drill bit 502, relative to cam assembly 580 and drillstring 506. In such an embodiment, the rotating motion of drill bit 502and torque-applying structure 560 coupled thereto may cause cam followerassembly 590 to rotate or change position relative to cam assembly 580.For example, as detailed above, first end 562 of torque-applyingstructure 560 may be attached, affixed, connected, coupled to, incontact with, or engaged with a portion of cam follower assembly 590(e.g., cam follower elements 594). Accordingly, as drill bit 502 (andtorque-applying structure 560 coupled thereto) rotates, the first end562 of torque-applying structure 560 may cause cam follower assembly 590to rotate relative to cam assembly 580.

As detailed above, cam follower assembly 590 may be structured tocontact, trace, or follow the cam surface 581 of cam assembly 580. Forexample, in the exemplary embodiment illustrated in FIG. 11A, camfollower elements 594 of cam follower assembly 590 may generally contactand thus follow or trace cam surface 581 of cam assembly 580. In atleast one embodiment, as cam follower assembly 590 traces or follows camsurface 581 of cam assembly 580 during rotation of rotary drill bit 502,the rise and fall (with respect to direction D₁ in FIG. 1) of camsurface 581 may also cause torque-applying structure 560 to be loweredand raised in a generally cyclic or reciprocating motion. Moreparticularly, as shown in FIG. 12A, torque-applying structure 560 mayreciprocate toward and away from cutting element 570 during rotation ofdrill bit 502, thus causing the second end 564 of torque-applyingstructure 560 to engage and disengage, in turn, engaging features 575 ofcutting element 570. In at least one embodiment, torque-applyingstructure 560 may be structured so that, as second end 564 oftorque-applying structure 560 engages an engaging feature 575 of cuttingelement 570, torque-applying structure 560 applies torque to cuttingelement 570 to cause cutting element 570 to rotate within cutting pocket515 of drill bit 502. Accordingly, the exemplary configurationillustrated in FIG. 11A may utilize the rotary motion of drill bit 502to apply torque to cutting element 570.

In certain embodiments, cam assembly 580, cam follower assembly 590,torque-applying structure 560, and/or cutting element 570 may beconfigured so that cutting element 570 rotates in a selected manner(e.g., over selected periodic increments, over a selected angle, in aselected direction, or combination of the foregoing). More specifically,for example, as illustrated in FIGS. 11A and 12A, the second end 564 oftorque-applying structure 560 may engage and disengage, in turn,engaging features 575 of cutting element 570 as the rotary drill bit 502rotates relative to cam assembly 580 and drill string 506, periodicallyapplying torque to cutting element 570 to cause cutting element 570 torotate within cutting pocket 515 of drill bit 502. For example,torque-applying structure 560 may engage and apply torque to (and thuscause the rotation of) cutting element 570 as cam follower elements 594(and thus torque-applying structure 560) rise, in direction D₁ in FIG.11A, in response to an inclined portion of cam surface 581 of camassembly 580. Subsequently, torque-applying structure 560 may disengage(and thus cease application of torque to) cutting element 570 as camfollower elements 594 of cam follower assembly 590 are lowered (i.e.,moved in a generally opposite direction to direction D₁ shown in FIG.11A) in response to a declined portion of cam surface 581 of camassembly 580.

In at least one embodiment, cutting element 570 may be inhibited orlimited from rotating in a direction opposite to the intended directionof rotation caused by torque applied by a torque-applying structure. Forexample, as illustrated in FIG. 12B, a limiting member 561 may be biasedtoward and may engage engaging features 575 of cutting element 570 toinhibit cutting element 570 from rotating in a direction opposite to theintended direction of rotation caused by torque applied bytorque-applying structure 560. Limiting member 561 may be any structureor assembly structured for limiting the rotation of cutting element 570in an undesired direction. In at least one embodiment, limiting member561 may be housed in a recess or aperture defined in bit body 510 ofdrill bit 502.

In at least one embodiment, and as illustrated in FIG. 15A,torque-applying structure 560 may be biased towards cam followerassembly 590 so that, when cam follower elements 594 of cam followerassembly 590 are lowered in response to a declined portion of the camsurface 581 of cam assembly 580, torque-applying structure 560 remainsin contact with cam follower elements 594 of cam follower assembly 590.In the exemplary embodiment illustrated in FIG. 15A, torque-applyingstructure 560 may be biased towards cam follower element 594 by abiasing element 568. Biasing element 568 generally represents any typeor form of structure capable of biasing torque-applying structure 560towards cam follower element 594; including, for example, a spring orsimilar structure. In certain embodiments, biasing element 568 may be incontact with both bit body 510 of drill bit 502 and the first end 562(e.g., substrate 563) of torque-applying structure 560.

As detailed above, first end 562 of torque-applying structure 560 may beattached, affixed, connected, coupled to, in contact with, or configuredto interact with a portion of cam follower assembly 590, such as camfollower elements 594, in any number of ways. For example, asillustrated in FIG. 15B, in at least one embodiment the first end 562 oftorque-applying structure 560 may be disposed and retained within arecess 596 defined within an inclined portion 598 of cam followerelement 594. In certain embodiments, one or more retention elements 591may retain first end 562 of torque-applying structure 560 within portion598 of cam follower element 594.

As detailed above, and as illustrated in FIGS. 15A and 15B, a recess 596defined in each cam follower element 594 may be structured to receive orcouple to the first end 562 of torque-applying structure 560. Recess 596may exhibit any selected shape and size. For example, as seen in FIGS.14A, 14C, 15A, and 15B, recess 596 may be generally hemispherical inshape or curved, rounded, or radiused. This exemplary configuration mayallow first end 562 of torque-applying structure 560 to pivot or swivelwithin recess 596 as cam follower elements 594 rise and fall (generallywith respect to direction D₁ in FIG. 11A) while tracing or following thecam surface 581 of cam assembly 580.

The exemplary configuration of drilling system 500 illustrated in FIG.11A may provide a number of advantages and benefits. For example, if asurface area of cam follower elements 594 is greater than a surface areaof the first end 562 of torque-applying structure 560, cam followerelements 594 may decrease the force and/or stress applied to cam surface581 of cam assembly 580 (e.g. cam inserts 584). Such a configuration mayslow the rate of wear and increase the life of cam assembly 580 (e.g.,cam surface 581 and/or cam inserts 584). In addition, connectingstructure 592 of cam follower assembly 590 may increase the stability ofdrilling system 500 by keeping cam follower elements 594 in generalalignment with both torque-applying structure 560 and cam assembly 580.

FIGS. 16A-16C illustrate an exemplary cutting element 570 andtorque-applying structure 560 according to at least one additionalembodiment. As with previous embodiments, cutting element 570 may beformed of any material or combination or materials suitable for cuttingrock or other subterranean formations. For example, cutting element 570may be substantially comprised of a selected material (e.g., asuperabrasive material without a substrate). Alternatively, in at leastone example, and as illustrated in FIGS. 16A-16C, cutting element 570may comprise a superabrasive layer or table 574 bonded to or formed upona substrate 572. Table 574 may be formed of any material or combinationof materials; including, for example, a superhard or superabrasivematerial, such as polycrystalline diamond. Similarly, substrate 572 maycomprise any material capable of adequately supporting a superabrasivematerial during drilling of a subterranean formation; including, forexample, cemented tungsten carbide.

In at least one example, cutting element 570 may be bonded, adhered, orattached to a clutch structure 540. In one embodiment, clutch structure540 may be integrally formed with, or represent a portion of cuttingelement 570. For example, substrate 572 may comprise a clutch structure540, as opposed to being adhered, bonded, or attached to clutchstructure 540 that is external to substrate 572. Clutch structure 540generally represents any type or form of mechanical device or structurefor selectively connecting and/or disconnecting a force or torquegenerating system and cutting element 570. In other words, clutchstructure 540 may be configured to selectively allow or inhibitapplications of a force or a torque to cutting element 570, bydisengaging when a specified level of torque is reached (e.g., toprotect a torque-applying member 560 from excessive force, etc.). Asillustrated in FIGS. 16A-16C, clutch structure 540 may comprise a firstportion 541 and a second portion 542. In certain embodiments, firstportion 541 may be at least temporarily coupled to second portion 542 byfrictionally contacting, interlocking with, meshing with, engaging, orcontacting second portion 542.

As illustrated in FIGS. 16A-16C, first portion 541 may comprise a firstengaging surface 543 structured to frictionally contact and/ormechanically engage, a second engaging surface 544 provided on secondportion 542. In the exemplary embodiment illustrated in FIG. 16B, firstengaging surface 543 may comprise at least one first engaging structure545 structured to mechanically engage at least one complimentary secondengaging structure 546 provided on second engaging surface 544. Firstengaging structure 545 and second engaging structure 546, each of whichgenerally represents any type or form of structure capable of engaging acorresponding structure, may be formed in any geometrical shape or size.For example, as illustrated in FIG. 16B, a plurality of tooth-shapedsecond engaging structures 546 provided on second portion 542 may beconfigured to interlock with, mesh with, engage, or contact a pluralityof corresponding first engaging structures 545 provided on first portion541.

In an additional embodiment, first portion 541 and second portion 542may comprise disc-shaped friction members capable of being brought intocontact with one another by one or more biasing members (e.g., one ormore springs, spring washers, etc.). In this exemplary embodiment, asillustrated in FIG. 16C, a first friction material 547 may be formed onfirst portion 541, while a second friction material 548 may be formed onsecond portion 542. Friction materials 547 and 548 may comprise anymaterial or combination of materials capable of frictionally engaging anopposing material or structure. As illustrated in FIG. 16C, at least onespring element 550 (e.g., one or more springs, coil springs, Bellevillewasher springs, etc.) may be positioned between a front surface ofcutting pocket 515 (surface facing in direction D₃) and a back surfaceof second portion 542 (surface facing opposite direction D₃) to bringfirst engaging surface 543 of first friction material 547 into contactwith second engaging surface 544 of second friction material 548. Incertain embodiments, when the first engaging surface 543 of firstfriction material 547 is brought into contact with the second engagingsurface 544 of second friction material 548, first portion 541 may becoupled to second portion 542, enabling rotation of cutting element 570by torque-applying structure 560. At least one biasing element 549(e.g., one or more springs, coil springs, Belleville washer springs,etc.) may also be positioned between second end 577 of couplingstructure 576 and bit body 510 of bit 502 to bias cutting element 570toward cutting pocket 515 (in a direction generally opposite todirection D₃ as shown in FIG. 16C).

In at least one embodiment, first portion 541 of clutch 540 may at leastpartially disengage from second portion 542 of clutch 540 when aresistive force transmitted to first portion 541 exceeds the mechanicalengagement force between first portion 541 and second portion 542. Asexplained above, one or more torque-generating and/or torque-applyingstructures or assemblies may be configured to apply torque to cuttingelement 570. For example, as illustrated in FIG. 16A, second end 564 oftorque-applying structure 560 may apply torque to second portion 542 ofclutch portion 540. Because second portion 542 is mechanically engagedwith first portion 541, the torque applied by torque-applying structure560 to second portion 542 may cause second portion 542 and, in turn,first portion 541 (and accordingly cutting element 570) to rotate.However, in certain situations, a resistive force (e.g., cutting forces,friction, etc.) applied to cutting element 570 (e.g., a cutting forceapplied to table 574 of cutting element 570 by a subterranean formation)may inhibit or prevent rotation of cutting element 570. In an examplewhere rotation of cutting element 570 is inhibited or prevented, secondportion 542 and first portion 541 may disengage from one another at aselected force or torque, thus allowing second portion 542 to continueto rotate in response to torque applied by torque-applying structure 560while first portion 541 remains stationary. When rotation of cuttingelement 570 is inhibited, causing second portion 542 to disengage fromfirst portion 541, spring element 550 may compress to allow secondportion 542 to rotate in cutting pocket 515 independently of firstportion 541.

In at least one embodiment, as illustrated in FIG. 16B, the geometricalshape of first engaging structures 545 and second engaging structures546 may allow second portion 542 to slip or disengage from first portion541 of clutch 540 under selected conditions. In other words, thegeometrical shape of first engaging structures 545 and second engagingstructures 546 may be configured to provide a selected minimum force ortorque at which second portion 542 may disengage from first portion 541.In addition, a biasing element may be provided to apply a selectedamount of force between first portion 541 and second portion 542.

In an additional embodiment, first friction material 547 and secondfriction material 548 may be configured to provide a selected minimumforce at which second portion 542 may disengage from first portion 541.For example, as illustrated in FIG. 16C, first friction material 547 andsecond friction material 548 may provide sufficient frictional force tomaintain first engaging surface 543 in contact with second engagingsurface 544 during the rotation of second portion 542 by torque-applyingstructure 560 up to a selected minimum force or torque. The exemplaryembodiments illustrated in FIGS. 16A-16C may thus prevent damage to oneor more portions of the drilling system by allowing second portion 542to continue to rotate in response to torque applied to second portion542, while permitting first portion 541 to remain stationary.

FIG. 17 is a cross-sectional side view of an exemplary cutting element670 according to an additional embodiment. As with previous embodiments,cutting element 670 may be formed of any material or combination ormaterials used for cutting formations. For example, cutting element 670may comprise any suitable material in a desired configuration or aplurality of materials, without limitation. In at least one example, andas illustrated in FIG. 17, cutting element 670 may comprise asuperabrasive layer or table 674 bonded to or formed upon a substrate672. Table 674 may be formed of any suitable superabrasive material;including, for example, polycrystalline diamond. Similarly, substrate672 may comprise any material or combination of materials capable ofadequately supporting a superabrasive material (e.g., during drilling ofa subterranean formation); including, for example, materials such ascemented tungsten carbide.

In at least one example, substrate 672 of cutting element 670 may beadhered, brazed, welded, or affixed to a base member 678. Base member678 may be formed in any shape or size and of any material orcombination or materials. For example, base member 678 may comprise oneor more metals, such as, for example, steel. In certain embodiments, thematerials comprising substrate 672 of cutting element 670 may be chosenbased on the coefficient of thermal expansion of the material ormaterials comprising base member 678. For example, substrate 672 maycomprise tungsten carbide having a concentration of cobalt that resultsin substrate 672 having a coefficient of thermal expansion thatgenerally corresponds to a coefficient of thermal expansion of basemember 678.

In at least one embodiment, a recess 679 may be defined in base member678. As illustrated in FIG. 17, recess 679 may comprise threadsstructured to receive and engage coupling structure 676, which may alsobe threaded (e.g., a first end 675 of coupling structure 676 may bethreaded into recess 679 of base member 678). Coupling structure 676generally represents any type or form of structure capable of couplingcutting element 670 to bit body 610 (e.g., the face or blades of body610). In at least one embodiment, coupling structure 676 may comprise asecond end 677 that is larger than an aperture 617 defined in bit body610 so that, once first end 675 of coupling structure 676 is threadedinto recess 679, cutting element 670 may be effectively retained withina cutting pocket 615 defined in bit body 610 of drill bit 602. A biasingelement 690 (e.g., a Belleville washer spring, a coil spring, etc.) mayalso be positioned between the second end 677 of coupling structure 676and the bit body 610 of drill bit 602 to bias cutting element 670 towardcutting pocket 615.

As shown in FIG. 17, a separation element 665 (e.g., a washer or otherelement) may be positioned between a front surface of cutting pocket 615(e.g., a surface facing generally in direction D₃) and a back surface ofcutting element 670 (e.g., a surface facing in a direction generallyopposite to direction D₃). Separation element 665 may comprise a washeror a layer of material, such as a metal or ceramic shim. In anotherembodiment, separation element 665 may be configured to reduce frictionand/or wear between cutting element 670 and cutting pocket 615.Optionally, separation element 665 may be sacrificial (i.e., may besofter than cutting element 670 and/or cutting pocket 615).

In another embodiment, a coating, such as diamond, silicon carbide,chrome, tungsten carbide, etc., may be deposited (e.g., electroplated,thermally sprayed, sputtered, electrolessly deposited, or formed ordeposited) upon at least a portion of cutting pocket 615 and/or cuttingelement 670. For example, at least a portion of base member 678 may becoated with an erosion resistant material, such as a homogeneous,binder-free tungsten carbide material. In at least one embodiment, thiserosion resistant material may increase the hardness of, slow the wearof, and increase the overall life of base member 678.

FIG. 18A is a cross-sectional side view of an exemplary cutting element770, torque-amplifying assembly 730, and torque-applying structure 760according to at least one embodiment. Cutting element 770 generallyrepresents any type or form of cutting element capable of cutting asubterranean formation; including, for example, PDC cutters. As withprevious embodiments, cutting element 770 may be formed in any number ofconfigurations and of any material or combination or materials. Forexample, in certain embodiments (and as illustrated in FIG. 18A),cutting element 770 may comprise a layer or table 774 bonded to orformed upon a substrate 772. Optionally, as with all previousembodiments, cutting element 770 may comprise a superabrasive structureformed without a substrate, the superabrasive material comprising, forexample, diamond, silicon carbide, boron nitride, or a combination ofthe foregoing. Cutting element 770 may also comprise a superabrasivetable bonded to a substrate.

Table 774 in FIG. 18A may comprise any material or combination ofmaterials used for cutting formations; including, for example, asuperhard or superabrasive material such as polycrystalline diamond.Similarly, substrate 772 may comprise any material or combination ofmaterials capable of adequately supporting a superabrasive materialduring drilling of a subterranean formation; including, for example,cemented tungsten carbide. For example, cutting element 770 may includea table 774 comprising polycrystalline diamond bonded to a substrate 772comprising cobalt-cemented tungsten carbide.

In another aspect of the invention, a torque-amplifying assembly may beemployed. A torque-amplifying assembly may be any type or form ofstructure or assembly capable of amplifying, multiplying, or increasinga torque. In at least one embodiment, at least a portion of an exemplarytorque-amplifying assembly 730 may be disposed within or coupled to aportion of bit body 710 (e.g., the blades of bit body 710). For example,as illustrated in FIG. 18A, torque-amplifying assembly 730 may bedisposed within an aperture or a plurality of apertures or recessesdefined in bit body 710.

In at least one embodiment, torque-amplifying assembly 730 may comprisea harmonic gear or planetary gear system. For example, torque-amplifyingassembly 730 may comprise a first gear and at least a second gear. Asillustrated in FIG. 18A, torque-amplifying assembly 730 may comprise afirst gear 750 engaged or mechanically coupled to a second gear 755.First gear 750 and second gear 755, which generally represent any typeor form of gear structure or assembly, may be formed in any selectedshape and size and may comprise any suitable material. In at least oneembodiment, first gear 750 may be coupled to a torque-generatingassembly (such as, for example, cam assembly 580 and cam followerassembly 590 in FIG. 11A) via a torque-applying structure (such as, forexample, torque-applying structure 760). First gear 750 may be coupledto a torque-generating assembly in any number of ways and in any numberof configurations. In one example, first gear 750 may be affixed,connected, or attached to a shaft 778 disposed within bit body 710. Inat least one embodiment, one or more shaft bearings or bushings 747 maybe operably coupled to shaft 778 (e.g., the ends of shaft 778) to allowshaft 778 to rotate within bit body 710.

In at least one embodiment, as illustrated in FIG. 18A, shaft 778 may beintegrally formed with, or affixed or attached to, a rotatable structure740. Rotatable structure 740 represents any type or form of mechanismconfigured to allow rotation in a selected direction and limit rotationin an opposite direction (e.g., a ratchet structure, etc.). Such amechanism may cause rotation in the selected direction to occur in stepsor intervals. In at least one additional embodiment, rotatable structure740 may comprise one or more engaging features 745. As with previousembodiments, engaging features 745 generally represent any type or formof structure or recess capable of engaging or receiving an opposingstructure, such as the second end 764 of torque-applying structure 760.Examples of engaging features 745 include, without limitation, recesses,protuberances, gear teeth, or any other suitable structure or aperture.

In at least one embodiment, second gear 755 of torque-amplifyingassembly 730 may be adhered, brazed, welded, affixed, or coupled tocutting element 770. For example, as illustrated in FIG. 18A, secondgear 755 may be brazed to the bottom surface of substrate 772 of cuttingelement 770. In addition, as illustrated in FIG. 18A, second gear 755and cutting element 770 may be coupled to bit body 710 (e.g., a blade ofbit body 710) by a coupling structure 776. Coupling structure 776 may beany type or form of structure capable of coupling cutting element 770and/or second gear 755 to bit body 710 (e.g., the face or blades of bitbody 710). In at least one embodiment, coupling structure 776 maycomprise a second end 777 that is larger than an aperture 717 defined inbit body 710 so that, once the first end of coupling structure 776 isattached to cutting element 770, cutting element 770 may be effectivelyretained within a cutting pocket 715 defined in bit body 710. A biasingelement (such as biasing element 590 in FIG. 12A) may optionally bepositioned between the second end 777 of coupling structure 776 and bitbody 710 to bias cutting element 770 toward cutting pocket 715.

In at least one embodiment, first gear 750 may rotate in response totorque applied by a torque-applying structure (such as, for example,torque-applying structure 760). For example, second end 764 oftorque-applying structure 760 may engage engaging features 745 and applytorque generated by a torque-generating assembly to rotatable structure740, causing rotatable structure 740, shaft 778, and first gear 750coupled thereto to rotate in a first direction. As illustrated in theside view of FIG. 18B, the rotary motion of first gear 750 may in turncause second gear 755 (and cutting element 770 affixed thereto) torotate in a second direction that is opposite to the first direction ofrotation of first gear 750.

In at least one embodiment, the gear ratio between first gear 750 andsecond gear 755 may be chosen so that the amount of torque applied tocutting element 770 via second gear 755 is increased. For example, asillustrated in FIG. 18B, the number of teeth 756 on second gear 755 maybe greater than the number of teeth 752 on first gear 750. In certainembodiments, the greater number of teeth and greater radius or size ofsecond gear 755 may slow the speed of rotation of second gear 755 (andthus cutting element 770 attached thereto), while increasing the amountof torque (in relation to torque applied to first gear 750) that isapplied to cutting element 770. The exemplary torque-amplifying assembly730 illustrated in FIGS. 18A and 18B may thus increase the amount oftorque generated by a torque-generating assembly that is ultimatelyapplied to cutting element 770.

FIG. 19 is a perspective side view of an exemplary cutting elementassembly 870 and torque-applying structure 860 according to at least oneadditional embodiment. As seen in FIG. 19, in certain embodiments,cutting element assembly 870 may comprise at least two cutting elements;namely, 870A, 870B, and 870C. Cutting elements 870A, 870B, and 870C maycomprise any type or form of cutting element capable of cutting asubterranean formation; including, for example, PDC cutters (e.g.cutting element 570 in FIG. 11A). For example, in certain embodiments,cutting elements 870A, 870B, and 870C may comprise a superabrasive layeror table bonded to or formed upon a substrate. Optionally, cuttingelements 870A, 870B, and 870C may be initially formed without asubstrate and may include, for example, diamond, silicon carbide, boronnitride, a combination of the foregoing, etc. In certain embodiments,cutting elements 870A, 870B, and 870C may be rotatably mounted to a bitbody of a drill bit (such as, for example, bit body 510 of drill bit 502in FIG. 11A).

In at least one embodiment, cutting element 870A may contact or engageengaging features 845 of torque-applying wheel 840. For example, cuttingelement 870A may comprise one or more engaging features 875 configuredor structured to engage one or more engaging features 845 provided ontorque-applying wheel 840. As with previous embodiments, engagingfeatures 875 and engaging features 845 each generally represent any typeor form of structure or recess capable of engaging or receiving acomplementary structure. Examples of engaging features 875 and engagingfeatures 845 include, without limitation, recesses, protuberances, gearteeth, or any other suitable structure or aperture. Torque-applyingwheel 840 may generally represent any mechanism configured to applytorque to a structure. In certain embodiments, torque-applying wheel 840may be configured to rotate in a selected direction and limit rotationin an opposite direction. Such a mechanism may cause rotation in theselected direction to occur in steps or intervals. In at least oneembodiment, torque-applying wheel 840 may rotate in response to torqueapplied by torque-applying structure 860. As illustrated in FIG. 19, therotary motion of torque-applying wheel 840 may in turn cause cuttingelement 870A to rotate in a direction opposite to the direction ofrotation of torque-applying wheel 840.

In at least one embodiment, cutting element 870A may also contact orengage at least one additional cutting element, such as cutting element870B and/or cutting element 870C. For example, as illustrated in FIG.19, the engaging features 875 provided on cutting element 870A mayengage or contact engaging features 875 provided on cutting element 870Band/or cutting element 870C. As illustrated in FIG. 19, cutting element870A may cause, in response to torque applied by torque-applying wheel840, cutting element 870B and/or cutting element 870C to rotate in adirection that is opposite to the direction of rotation of cuttingelement 870A. Thus, as illustrated in FIG. 19, a single torque-applyingstructure 860 (such as, for example, a push rod) and rotatable structure(such as, for example, torque-applying wheel 840) may be used to applytorque to, and rotate, more than one cutting element (such as cuttingelements 870A, 870B, and/or 870C).

FIG. 20 is a cross-sectional side view of an exemplary drill bit body910 and torque-applying structure 960 according to an additionalembodiment. Torque-applying structure 960 generally represents anystructure or assembly capable of applying torque to at least a portionof a cutting element. For example, as illustrated in FIG. 20,torque-applying structure 960 may be a push rod structured to applytorque to a cutting element (such as, for example, cutting element 570in FIG. 11A).

In at least one embodiment, torque-applying structure 960 may beattached, connected, disposed within, or coupled to bit body 910. Forexample, as illustrated in FIG. 20, torque-applying structure 960 may bedisposed within a passageway 915 defined in bit body 910. In certainembodiments, torque-applying structure 960 may also be coupled to apressure-compensating assembly 920. Pressure-compensating assembly 920generally represents any structure or assembly capable of at leastpartially compensating for, or equalizing, differences in pressureexternal to a sealed chamber (typically containing a lubricant) withinbit body 910.

In further detail, as illustrated in FIG. 20, pressure-compensatingassembly 920 may comprise a lubricating fluid 924 disposed within achamber 927 defined by at least a portion of a reservoir 925, at least aportion of passageway 915 between seal members 922, and a conduit 923connecting reservoir 925 and passageway 915. In at least one embodiment,lubricating fluid 924 may be retained within chamber 927 by at least oneseal member 922. Seal members 922, which may exhibit any shape and/orsize and may comprise any suitable material, may be any sealingstructure or assembly capable of forming a mechanical seal. For example,in at least one embodiment, at least one of seal members 922 maycomprise an elastomeric o-ring, a metal seal, or the like. In certainembodiments, at least one of seal members 922 may prevent debris fromentering chamber 927.

As illustrated in FIG. 20, reservoir 925 may comprise an opening definedin bit body 910 that is connected to passageway 915 by conduit 923. Inat least one embodiment, reservoir 925 may be open to an externalportion of bit body 910. In addition, pressure-compensating assembly 920may comprise a dynamic member 926 disposed within reservoir 925 thatseparates lubricating fluid 924 in chamber 927 from a portion ofreservoir 925 that is open to an external portion of bit body 910.Dynamic member 926 may represent any structure or assembly capable offlexing, bending, moving, or accommodating differences between apressure external to bit body 910 and a pressure within chamber 927. Inat least one embodiment, dynamic member 926 may comprise a flexiblediaphragm that flexes in response to a difference in pressure on eitherside of dynamic member 926. For example, a dynamic member 926 comprisinga flexible diaphragm may flex or otherwise deform in response to adifference between an internal pressure P_(A) and a pressure P_(B)external to bit body 910. More particularly, as illustrated in FIG. 20,a dynamic member 926 comprising a flexible diaphragm may flex generallyin a direction D₄ when pressure P_(A) exceeds pressure P_(B), andalternatively, may flex generally in a direction opposite direction D₄when pressure P_(B) exceeds pressure P_(A).

In an additional embodiment, dynamic member 926 may comprise a pistonthat moves in response to a pressure differential between pressure P_(A)and pressure P_(B). Specifically, a dynamic member 926 comprising apiston may move in direction D₄ when pressure P_(A) exceeds pressureP_(B), and alternatively, may move in a direction opposite direction D₄when pressure P_(B) exceeds pressure P_(A). Accordingly, dynamic member926 may at least partially compensate for, or at least partiallyequalize, a difference between internal pressure P_(A) and a pressureP_(B) external to bit body 910.

FIGS. 21A-21F illustrate an exemplary drilling system 1000 according toat least one additional embodiment. As illustrated in FIG. 21A,exemplary drilling system 1000 may comprise a drill bit 1002 having abit body 1010. Drill bit 1002 may represent any type of earth-boring ordrilling tool; including, for example, core bits, roller-cone bits,fixed-cutter bits, eccentric bits, bi-center bits, reamers, reamerwings, and the like. Drill bit 1002 may also be formed in any number ofways and of any suitable material. For example, drill bit 1002 may bemachined from steel or may be manufactured by infiltrating a binder intoa tungsten carbide particulate, as described above.

As shown in FIG. 21A, one or more rotatable cutting elements 1070 and/orone or more fixed (i.e., stationary) cutting elements 1071 may bemounted to the face or blades of bit body 1010 of drill bit 1002.Generally speaking, cutting elements 1070 and 1071 may comprise anycutting element capable of cutting a subterranean formation. As withprevious embodiments, cutting elements 1070 and 1071 may be formed ofany material or combination or materials suitable for cuttingformations. For example, as illustrated in FIG. 21B, cutting element1070 may comprise a superabrasive layer or table 1074 bonded to orformed upon a substrate 1072. Table 1074 may be formed of any materialor combination of materials; including, for example, a superhard orsuperabrasive material, such as polycrystalline diamond. Similarly,substrate 1072 may comprise any material capable of adequatelysupporting a superabrasive material during drilling of a subterraneanformation; including, for example, cemented tungsten carbide.

Cutting element 1070 may be rotatably mounted to bit body 1010 of drillbit 1002 in any number of ways and configurations. For example, asillustrated in FIG. 21B, cutting element 1070 may be rotatably mountedto drill bit 1002 by adhering, brazing, threadedly affixing, welding, orsecuring cutting element 1070 to a first end 1077 of a connecting member1076. In at least one embodiment, and as described in greater detailbelow, a second end 1078 of connecting member 1076 may be coupled to atorque-generating assembly. Cutting element 1070 may be positionedwithin a cutting pocket (such as cutting pocket 515 in FIG. 12A)comprising a recessed space or aperture open to an outside portion ofbit 1002.

In at least one embodiment, cutting element 1070 may rotate in responseto torque generated and applied to cutting element 1070 by atorque-generating assembly. In the exemplary embodiment illustrated inFIGS. 21A-21F, this torque-generating assembly may comprise a camassembly 1080 coupled to a drill string (such as, for example, drillstring 506 in FIG. 11A), a cam follower assembly 1090 in contact with orcoupled to the cam assembly 1080, and a torque-applying structure 1060configured to transmit force from cam assembly 1080 to apply torque tocutting element 1070.

In at least one embodiment, cam assembly 1080 may comprise asubstantially annular-shaped cam body 1082. For example, as illustratedin FIG. 21E, cam body 1082 may be formed in the general shape of anannulus with an external surface 1087 and an internal surface 1089. Incertain embodiments, the radial width of cam body 1082 between externalsurface 1087 and internal surface 1089 may vary at different points oncam body 1082. In certain embodiments, as illustrated in FIG. 21E, aradius of internal surface 1089 and/or a radius of cam surface 1081 mayvary as a function of angle θ with respect to an axis of rotation 1003around which rotary drill bit 1002 may rotate. For example, radius R₁ ofcam surface 1081 at angle θ₁ may differ from radius R₂ of cam surface1081 at θ₂ (radius R₁ and R₂ are measured from the axis of rotation 1003to cam surface 1081, as shown in FIG. 21E).

As illustrated in FIG. 21E, cam body 1082 of cam assembly 1080 maycomprise a cam surface 1081. In certain embodiments, cam surface 1081may be formed of a single, unitary structure or material. In anadditional embodiment, cam surface 1081 may comprise the collectivesurfaces of a plurality of cam inserts 1084 affixed to the internalsurface 1089 of cam body 1082, as illustrated in FIGS. 21E and 21F. Caminserts 1084 may be formed in any number of configurations and of anymaterial or combination of materials. For example, in the exemplaryembodiment illustrated in FIG. 21E, cam inserts 1084 may comprise asuperabrasive insert or compact comprising a superabrasive layer ortable 1085 bonded to or formed upon a substrate 1083. In an additionalembodiment, cam inserts 1084 may each comprise a unitary or integrallyformed superabrasive structure comprising, for example, diamond, siliconcarbide, boron nitride, or a combination of the foregoing.

As with previous embodiments, table 1085 of cam inserts 1084 may beformed of any material or combination of materials; including, forexample, a superhard or superabrasive material such as polycrystallinediamond, silicon carbide, boron nitride, diamond, or any superabrasivematerial. Similarly, substrate 1083 may comprise any material orcombination of materials capable of adequately supporting asuperabrasive material; including, for example, cemented tungstencarbide. For example, cam insert 1084 may comprise a table 1085comprising polycrystalline diamond bonded to a substrate 1083 comprisingcobalt-cemented tungsten carbide. In addition, as explained above, afterformation of table 1085, a catalyst material (e.g., cobalt, nickel,etc.) may be at least partially removed (e.g., by acid-leaching) fromtable 1083.

As seen in FIGS. 21E and 21F, each cam insert 1084 may be structured andpositioned proximate to an adjacent cam insert 1084 to form cam surface1081. In an additional embodiment, each cam insert 1084 may abut (e.g.,along an arcuate side surface, along a concave side surface, etc.)and/or partially surround a circumferentially adjacent cam insert 1084.Each cam insert 1084 may be formed in any shape or size. For example,cam inserts 1084 may be generally rounded or generally rectangular orformed in any other shape. Cam inserts may be machined to form asubstantially cylindrical cam 1081.

In at least one embodiment, cam inserts 1084 of cam assembly 1080 maydiffer slightly in size and shape from each other. In an additionalembodiment, each cam insert 1084 may be formed to have a heightsubstantially the same as its circumferentially adjacent inserts. Forexample, as illustrated in FIG. 21E, a plurality of substantiallyidentical cam inserts 1084 having substantially identical heights may beaffixed to a cam body 1082. In this exemplary embodiment, each caminsert 1084 may be positioned and affixed within a cam insert pocket1088 defined in the cam body 1082. Cam insert pockets 1088 may bedefined in any shape and size and to any desired depth. In oneembodiment, the depth d₃ of each cam insert pocket 1088 defined in cambody 1082 may vary. In an additional embodiment, the depth d₃ of eachcam insert pocket 1088 defined in cam body 1082 may be substantiallyidentical, as illustrated in FIG. 21E.

In at least one embodiment, and as illustrated in FIGS. 21C, 21D, and21F, at least a portion of a cam follower assembly 1090 may be incontact with or coupled to cam surface 1081 of cam assembly 1080. Camfollower assembly 1090 generally represents any type or form ofstructure or assembly for contacting, tracing, or following the camsurface 1081 of cam assembly 1080. As illustrated in FIGS. 21B-21D and21F, cam follower assembly 1090 may comprise a pivot arm 1092 having afirst end 1093 and a second end 1095. In at least one embodiment, pivotarm 1092 may be pivotably mounted to bit body 1010 of bit 1002. Forexample, as illustrated in FIGS. 21B-21D, pivot arm 1092 may bepivotably mounted to bit body 1010 by inserting a pivot member 1011attached to, or integrally formed with, bit body 1010 through a recess1096 defined in pivot arm 1092.

As illustrated in FIGS. 21B-21D, cam follower assembly 1090 may alsocomprise at least one cam follower element 1094 rotatably attached tofirst end 1093 of pivot arm 1092 by a pin 1091. Cam follower element1094 may be formed in any shape or size and may comprise any material orcombination of materials. For example, in at least one embodiment, camfollower element 1094 may comprise a table of superhard or superabrasivematerial (such as polycrystalline diamond, silicon carbide, boronnitride, or the like) bonded to a substrate (comprising, for example,cemented tungsten carbide). In an additional embodiment, cam followerelement 1094 may comprise a unitary or integrally formed structurecomprising, for example, diamond, boron nitride, silicon carbide, or acombination of the foregoing.

As illustrated in FIGS. 21B-21D, second end 1095 of pivot arm 1092 ofcam follower assembly 1090 may be connected, attached, affixed, orcoupled to torque-applying structure 1060. For example, as illustratedin these figures, second end 1095 of pivot arm 1092 may be rotatablyattached to torque-applying structure 1060 by a connecting structure1013 inserted through apertures defined in both a body 1064 oftorque-applying structure 1060 and the second end 1095 of pivot arm1092.

Torque-applying structure 1060, which may be formed in any shape or sizeand of any material or combination of materials, generally representsany type or form of device or structure capable of applying torque to atleast a portion of a cutting element. For example, torque-applyingstructure 1060 may comprise a ratchet device or any mechanical device ormechanism capable of rotating a cutting element. As illustrated in FIGS.21C and 21D, torque-applying structure 1060 may comprise body 1064, atorque-applying wheel 1062, and a pawl 1066. In at least one embodiment,torque-applying wheel 1062, which may be formed in any shape and sizeand of any material, may be rotatably housed within a recess defined inbody 1064 of torque-applying structure 1060. Torque-applying wheel 1062also may be attached or connected to second end 1078 of connectingmember 1076 and configured to rotate independent of, and relative to,body 1064 of torque-applying structure 1060. In contrast, pawl 1066 maybe fixedly attached to, or integrally formed with, body 1064 oftorque-applying structure 1060. As illustrated in FIGS. 21C-21D, and asdescribed in greater detail below, pawl 1066 may comprise at least oneengaging structure 1067 configured to engage one or more engagingstructures 1063 formed on torque-applying wheel 1062.

In at least one embodiment, torque-applying structure 1060 may bestructured to apply a torque generated by a torque-generating assembly(comprising, for example, rotary drill bit 1002, cam assembly 1080,and/or cam follower assembly 1090) to cutting element 1070. For example,in certain embodiments bit body 1010 of rotary drill bit 1002 may bestructured to rotate relative cam assembly 1080, which may, as explainedabove, be coupled to a drill string (such as drill string 506 in FIG.11A). Since torque-applying structure 1060 and cam follower assembly1090 may be disposed within or coupled to bit body 1010 of drill bit1002, torque-applying structure 1060 and cam follower assembly 1090 mayalso rotate, in conjunction with drill bit 1002, relative to camassembly 1080.

As detailed above, cam follower assembly 1090 may be structured tocontact, trace, or follow cam surface 1081 of cam assembly 1080 as drillbit 1002 rotates relative to cam assembly 1080. For example in theexemplary embodiment illustrated in FIGS. 21C, 21D, and 21E, camfollower 1094 may contact and thus follow or trace the plurality of caminserts 1084 that comprise the cam surface 1081 of cam assembly 1080. Inat least one embodiment, an axis of rotation 1003 around which rotarydrill bit 1002 rotates may intersect the center of a generally circularshape defined by external surface 1087 of cam body 1082. Accordingly, ascam follower 1094 of cam follower assembly 1090 traces or follows thecam surface 1081 of cam assembly 1080 during rotation of rotary drillbit 1002, cam follower element 1094 may reciprocate (i.e., radiallyinwardly and radially outwardly) relative to pivot member 1011 as aresult of differences in the proximity of cam surface 1081 to the axisof rotation 1003 of rotary drill bit 1002. In other words, as rotarydrill bit 1002 (and cam follower assembly 1090 coupled thereto) rotatesrelative to cam assembly 1080, the proximity of cam surface 1081 to theaxis of rotation 1003 of rotary drill bit 1002 may change, which may inturn cause cam follower element 1094 to reciprocate relative to pivotmember 1011, as illustrated in FIGS. 21C and 21D. As detailed above, theproximity of cam surface 1081 to the axis of rotation 1003 of rotarydrill bit 1002 may vary based on the varying radial position or radialwidth (as defined by external surface 1087 and internal surface 1089) ofcam body 1082, as illustrated in FIG. 21E, and/or as a result ofdifferences in the height of cam inserts 1084 and/or cam insert pockets1088.

As illustrated in FIGS. 21C and 21D, the reciprocating motion of camfollower element 1084 may cause pivot arm 1092 of cam follower element1090 to pivot about pivot member 1011, as well as connecting structure1013 and pin 1091, which may in turn cause body 1064 of torque-applyingstructure 1060 and pawl 1066 to rotate in a first direction. As body1064 and pawl 1066 rotate, engaging structures 1067 of pawl 1066 mayengage one or more engaging structures 1063 formed on torque-applyingwheel 1062, causing torque-applying wheel 1062 (and second end 1068 ofconnecting member 1076 connected thereto) to rotate in a seconddirection opposite to the first direction. As torque-applying wheel 1062rotates, connecting member 1076, which is attached to torque-applyingwheel 1062, may transfer torque to cutting element 1070, causing cuttingelement 1070 to rotate. Accordingly, the exemplary embodimentsillustrated in FIGS. 21A-21F may utilize the rotary motion of drill bit1002 to apply torque to cutting element 1070.

Connecting member 1076 may comprise any type of connecting membercapable of transferring torque from torque-applying wheel 1062 tocutting element 1070; including, for example, a universal joint asillustrated in FIG. 21B. In addition, in at least one embodiment,cutting element 1070 may be inhibited or limited from rotating in adirection opposite to the direction of torque applied by torque-applyingwheel 1062. For example, a limiting member, such as a spring or othermechanism, may be biased toward and engage engaging features 1063 oftorque-applying wheel 1062 to inhibit cutting element 1070 from rotatingin a direction opposite to the direction of torque applied bytorque-applying wheel 1062. In certain embodiments, this limiting membermay be housed in a recess or aperture defined in body 1064 oftorque-applying structure 1060.

FIGS. 22A and 22B illustrate an exemplary drilling system 1100 accordingto an additional embodiment. As illustrated in FIG. 22A, exemplarydrilling system 1100 may comprise a drill bit 1102 having a bit body1110. Drill bit 1102 may represent any type of earth-boring or drillingtool; including, for example, core bits, roller-cone bits, fixed-cutterbits, eccentric bits, bicenter bits, reamers, reamer wings, and thelike. Drill bit 1102 may also be formed in any number of ways and of anytype of material or combination or materials. For example, drill bit1102 may be machined from steel or may be manufactured by infiltrating abinder into a tungsten carbide particulate, as described above.

In certain embodiments, one or more rotatable cutting elements 1170and/or one or more fixed (i.e., stationary) cutting elements 1171 may bemounted to the face or blades of bit body 1110 of drill bit 1102.Generally speaking, cutting elements 1170 and 1171 may comprise anycutting element capable of cutting a subterranean formation. As withprevious embodiments, cutting elements 1170 and 1171 may be formed ofany material or combination or materials suitable for cuttingformations. For example, cutting element 1170 may comprise a material ina substantially unitary configuration or may comprise a plurality ofmaterials (e.g., a superabrasive layer bonded to a substrate). In atleast one example, and as illustrated in FIG. 22B, cutting element 1170may comprise a superabrasive layer or table 1174 bonded to or formedupon a substrate 1172. Table 1174 may be formed of any material orcombination of materials; including, for example, a superhard orsuperabrasive material, such as polycrystalline diamond. Similarly,substrate 1172 may comprise any material capable of adequatelysupporting a superabrasive material during drilling of a subterraneanformation; including, for example, cemented tungsten carbide.

Cutting element 1170 may be rotatably mounted to bit body 1110 of drillbit 1102 in any number of ways and configurations. For example, asillustrated in FIG. 22B, cutting element 1170 may be rotatably mountedto drill bit 1102 by adhering, brazing, threadedly affixing, welding, orsecuring cutting element 1170 to a first end of a coupling structure1176. Coupling structure 1176 generally represents any structure capableof coupling cutting element 1170 a torque-generating assembly.

In at least one embodiment, rotatable cutting element 1170 may bestructured to rotate in response to a torque generated and applied by atorque-generating assembly. As illustrated in FIG. 22B, in certainembodiments this torque-generating assembly may comprise a hydraulicactuator assembly 1140 and a structural assembly 1150 coupled to boththe hydraulic actuator assembly 1140 and cutting element 1170. As withthe exemplary embodiments illustrated in FIGS. 4A-4C, hydraulic actuatorassembly 1140 may represent a device capable of converting hydraulic orpneumatic pressure generated by a pump, such as pump 130 in FIGS. 2 and3, into linear motion. In the exemplary embodiment illustrated in FIG.22B, hydraulic actuator assembly 1140 may comprise opposing seal members1142 disposed within a recess 1115 defined in bit body 1110, a chamber1143 defined by seal members 1142, a piston 1144 disposed within chamber1143, and a piston rod 1148 coupled to piston 1144.

In at least one embodiment, piston 1144 may be moved within chamber 1143by generating a pressure differential within chamber 1143. As detailedabove, in certain embodiments this pressure differential may begenerated by a pump, such as pump 130 in FIGS. 2 and 3. Chamber 1143 maybe in fluid communication with a pump used to generate this pressuredifferential, such as pump 130 in FIGS. 2 and 3, via one or moreconduits 1147. Conduits 1147 generally represent any type of fluidcommunication device; including, for example, hoses, pipes, and tubing.

In at least one embodiment, the movement of piston 1144 within chamber1143 may cause piston rod 1148, which may be coupled to piston 1144, toreciprocate in a linear fashion. In certain embodiments, structuralassembly 1150, which may be coupled to piston rod 1148, may convert thelinear motion of piston rod 1148 into rotary motion (i.e., torque) forrotating cutting element 1170. Structural assembly 1150, which may beformed in any shape and size, generally represents any device capable ofconverting linear motion generated by hydraulic actuator assembly 1140into rotary motion (i.e., torque) for rotating cutting element 1170. Inat least one embodiment, structural assembly 1150 may comprise aconnecting structure 1152 coupled to piston rod 1148 and a crank 1154coupled to both connecting structure 1152 and coupling structure 1176,which, as detailed above, may be coupled to cutting element 1170. Incertain embodiments, connecting structure 1152 may be coupled orattached to a first end of piston rod 1148. In addition, crank 1154 maybe rotatably attached to connecting structure 1152 by a pin 1156inserted through apertures defined in both connecting structure 1152 andcrank 1154.

In the exemplary embodiment illustrated in FIG. 22B, the linear motionof piston rod 1148 may be converted to rotary motion by structuralassembly 1150 by allowing crank 1154 to rotate about the axis of pin1156 as piston rod 1148, and connecting structure 1152 connectedthereto, reciprocates. This rotary motion may then be transferred fromcrank 1154 to coupling structure 1176, which may in turn apply thisrotary motion to cutting element 1170 as torque to rotate the cuttingelement.

In at least one embodiment, cutting element 1170 may be inhibited orlimited from rotating in a direction opposite to the direction of torqueapplied by a torque-applying structure, such as structural assembly1150. For example, a limiting member, such as a spring or othermechanism, may be biased toward and engage engaging features formed on aportion of coupling structure 1176 housed within crank 1154 to inhibitcoupling structure 1176, and thus cutting element 1170, from rotating ina direction opposite to the direction of torque applied by structuralassembly 1150. This limiting member may be any structure or assemblystructured for limiting the rotation of cutting element 1170 in anundesired direction. In certain embodiments, this limiting member may behoused in a recess or aperture defined in crank 1154 of structuralassembly 1150.

Rotation of a cutting element may be accomplished in variousconfigurations. For example, a cutting element may be rotated in a firstdirection (e.g., clockwise) and subsequently rotated in a seconddirection (e.g., clockwise or counterclockwise). In one embodiment, thesecond direction may be opposite to the first direction. In anotherembodiment, the second direction may be identical to the firstdirection. Further, as discussed above, a cutting element may be rotatedin a first direction and in a second direction opposite to the firstdirection through a selected angle (e.g., ninety degrees, forty-fivedegrees, one hundred and eighty degrees, etc.). In addition, rotation ofa cutting element may occur in a substantially continuous fashion or mayoccur in a stepped or piecewise fashion. Thus, a cutting element mayrotate and cease to rotate (or vice versa) if desired. Rotation mayoccur at any selected acceleration and/or velocity, without limitation.

Forces developed on a cutting element during drilling may inhibit orprevent rotation of the cutting element. Accordingly, it may beadvantageous to rotate a cutting element while limiting or preventingengagement of the cutting element with a material to be cut. Such aconfiguration may reduce or limit forces on the cutting element, whichmay limit or reduce resistance to rotation of the cutting element. Thus,in one embodiment, a cutting element may be employed for drilling asubterranean formation and periodically caused to have limited or nocontact with the subterranean formation. Such a method may facilitaterotation of the cutting element by limiting or eliminating resistance ofthe cutting element to rotation. Put another way, drilling operationsand/or conditions (e.g., weight on bit, torque, rotation speed (rpm),etc.) may be selected (e.g., periodically or according to any desiredcriteria, without limitation) for facilitating rotation of at least onerotatable cutting element.

The preceding description has been provided to enable others skilled inthe art to best utilize the invention in various embodiments and aspectsand with various modifications as are suited to the particular usecontemplated. This exemplary description is not intended to beexhaustive or to limit the invention to any precise form disclosed. Manymodifications and variations in the form and details are possiblewithout departing from the spirit and scope of the invention. It isintended that the scope of the invention be defined by the followingclaims.

1. A subterranean drilling system, comprising: a drill string; a rotarydrill bit coupled to the drill string, the rotary drill bit comprising:a bit body; and a cutting element coupled to the bit body, the cuttingelement being structured to rotate in response to torque applied to thecutting element; a cam assembly coupled to the drill string, the camassembly comprising a cam surface; a cam follower assembly in contactwith the cam surface of the cam assembly; and a torque-applyingstructure coupled to the cam follower assembly, the torque-applyingstructure configured to apply torque to the cutting element in responseto relative rotation between the cam assembly and the cam followerassembly.
 2. The drilling system of claim 1, wherein the cutting elementcomprises at least one engaging feature and the torque-applyingstructure comprises a push rod having a first end disposed within arecess defined in the cam follower assembly and a second end structuredto engage the at least one engaging feature of the cutting element. 3.The drilling system of claim 2, wherein the first end of the push rodcomprises a superabrasive material.
 4. The drilling system of claim 2,wherein the push rod is biased toward the cam follower assembly.
 5. Thedrilling system of claim 2, wherein the push rod comprises a flexibleportion and a substantially rigid portion.
 6. The drilling system ofclaim 1, wherein the cam follower assembly comprises at least one camfollower element.
 7. The drilling system of claim 6, wherein the camfollower element comprises a substrate and a superabrasive table bondedto the substrate.
 8. The drilling system of claim 1, wherein at least aportion of the cam follower assembly is pivotably attached to the bitbody.
 9. The drilling system of claim 8, wherein at least a portion ofthe cam follower assembly is rotatably attached to at least a portion ofthe torque-applying structure.
 10. The drilling system of claim 9,wherein at least a portion of the cam follower assembly pivots inresponse to relative rotation between the cam assembly and the camfollower assembly; and wherein at least a portion of the torque-applyingstructure rotates in response to relative rotation between the camassembly and the cam follower assembly.
 11. The drilling system of claim1, wherein the cutting element is limited from rotating in a selecteddirection.
 12. The drilling system of claim 1, wherein thetorque-applying structure is configured to cause the cutting element torotate in periodic increments.
 13. The drilling system of claim 1,wherein the torque-applying structure is configured to cause the cuttingelement to rotate continuously.
 14. The drilling system of claim 1,wherein the cutting element rotates within an angle of rotation of lessthan 360 degrees.
 15. The drilling system of claim 1, further comprisinga pressure-compensating assembly, the pressure-compensating assemblystructured to at least partially compensate for differences between apressure within at least a portion of the drill bit and another pressureexternal to at least a portion of the drill bit.
 16. The drilling systemof claim 15, wherein the pressure-compensating assembly comprises alubricating fluid within a sealed chamber, the sealed chamber beingdefined by at least one seal member and a dynamic member that isstructured to move in response to changes in pressure external to thesealed chamber.
 17. The drilling system of claim 1, wherein the camassembly comprises a plurality of cam inserts each affixed to a cambody, the plurality of cam inserts at least partially defining at leasta portion of the cam surface; and wherein at least one cam insert of theplurality of cam inserts at least partially surrounds an adjacent caminsert.
 18. The drilling system of claim 17, wherein the plurality ofcam inserts are substantially identical.
 19. The drilling system ofclaim 1, wherein the cam assembly comprises a cam body having asubstantially planar bottom surface; and wherein the cam surface of thecam assembly is angled with respect to the substantially planar bottomsurface of the cam body.
 20. The drilling system of claim 1, wherein thecam assembly comprises a substantially annular-shaped cam body; whereinthe cam surface comprises an internal surface of the cam body; whereinthe rotary drill bit is rotatable relative to an axis of rotation; andwherein a radial distance between the axis of rotation and the internalsurface of the cam body varies at different points on the internalsurface of the cam body.
 21. A subterranean drilling system, comprising:a drill string; a rotary drill bit coupled to the drill string, therotary drill bit comprising: a bit body; a first cutting element coupledto the bit body, the first cutting element being structured to rotate inresponse to torque applied to the cutting element; and a second cuttingelement coupled to the bit body; the second cutting element beingstructured to remain in a fixed position relative to the bit body; a camassembly coupled to the drill string, the cam assembly comprising a camsurface; a cam follower assembly in contact with the cam surface of thecam assembly; and a torque-applying structure coupled to the camfollower assembly, the torque-applying structure being configured toapply torque to the first cutting element in response to relativerotation between the cam assembly and the cam follower assembly.